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STRUCTURED FINANCE

Special Report

Moody’s Approach to Rating Multisector CDOs
AUTHORS:

CONTENTS

Jeremy Gluck, Ph.D.
Managing Director
(212) 553-3698
Jeremy.Gluck@
moodys.com

•

Summary

•

Overview: Motivation For Multisector CDOs

•

Measuring Diversity

•

Assessing Credit Quality: Default And Recovery Rates

•

Assessing Cash-Flow Characteristics

•

Conclusion

CONTACTS:

•

Appendixes I-IV

Gus Harris
Managing Director
(212) 553-1473
Gus.Harris@
moodys.com

SUMMARY

Helen Remeza, Ph.D.*
Vice President
Senior Analyst

Issac Efrat
Managing Director
(212) 553-7856
Issac.Efrat@
moodys.com
Investor Liaisons

Vernessa Poole
Asset-Backed
Securities and
Collateralized Debt
Obligations
(212) 553-4796
Vernessa.Poole@
moodys.com
Sally Cornejo
All Mortgage Related
and Fully Supported
Securities
(212) 553-4806
Sally.Cornejo@
moodys.com

The inclusion of an increasingly broad range of assets in Collateralized Debt
Obligation (CDO) collateral pools poses several analytical challenges. To analyze
diversification within a multisector CDO, Moody’s has established Asset Backed
Securities (ABS), Mortgage Backed Securities (MBS) and CDO sector classifications
in addition to those for existing corporate industries.
Within this classification scheme, Moody’s makes explicit assumptions about the
default correlation between assets to calculate a “diversity score,” a key determinant of credit enhancement. In addition, Moody’s recognizes that the loss severity
of a structured security varies by asset type, credit rating and position within the
capital structure. For asset types that are prepayment sensitive, maturity shortening
or extension risk due to faster or slower prepayment speed must be examined.
Several structural innovations have been developed for multisector CDOs. For
example, to deal with the issue of the longer Weighted Average Life (WAL) of the
CDO liabilities (which may result from long-maturity collateral), many multisector
deals include a step-up provision whereby the issuer is required to pay a hefty
margin to junior liability holders some years out. This gives the issuer a strong
incentive to call the deal prior to maturity, effectively shortening the WAL. Another
feature in some transactions is an option for the collateral manager to defease the
deal earlier than expected if the collateral performs very well. This again provides
the manager with the flexibility to unwind the transaction prior to maturity.
The CDO has emerged as an alternative vehicle for repackaging assets. As long as
the spreads on structured debt remain relatively wide, and while the interest in
reducing regulatory and economic capital costs is present, we expect to see a
stable flow of multisector transactions. Ultimately, this additional source of demand
for structured debt should spur the issuance of more ABS, MBS and CDOs.

* Helen Remeza contributed to this report while serving as a Senior Analyst within Moody’s Derivatives Team.
She is now at Credit Suisse First Boston.

September 15, 2000

OVERVIEW: MOTIVATION FOR MULTISECTOR CDOS
For more than a decade, participants in the CDO market have exploited the opportunity to
achieve arbitrage gains by securitizing illiquid high-yield bonds and leveraged loans. More
recently, they have turned their attention to the securitization of other illiquid instruments. In
some cases, the focus has been on even less liquid corporate bonds and loans, such as true
private placements or middle-market loans. In other cases, structured securities have become
prime candidates for inclusion in CDO collateral pools.
The spreads over Libor or other benchmarks for these less liquid instruments widened sharply
in Autumn 1998, when nearly all nongovernment security markets endured severe dislocations.
In the case of structured debt, spreads are still wide enough to fuel “resecuritization” transactions, in which structured instruments are repackaged via CDOs. Indeed, Moody’s has already
rated numerous transactions of this type.1

Choosing Collateral for Multisector CDOs2
ABS and MBS
Nearly all types of ABS and MBS have found their way into the
collateral pools of resecuritization CDOs.3 The senior tranches of
asset-backed transactions such as credit card and auto loan deals,
as well as those of residential mortgage transactions, are somewhat liquid and trade at tight spreads to Libor. However, the junior
tranches of nearly all ABS and MBS transactions are considerably
more illiquid and trade at a discount to like-rated corporate bonds,
making them attractive candidates for inclusion in arbitrageoriented CDOs. Newer transaction types, such as securitizations of
mutual fund fees, structured settlements, future flows, etc. also
lack liquidity, even at the senior-tranche level. Most Commercial
MBS (CMBS) tranches are also illiquid. Public deals are generally
more liquid, while 144A private placement transactions are often
less so, and “private private” (neither 144A nor Regulation S) transactions are still less liquid.
CDOs
Like the less standard forms of ABS, CDO tranches trade infrequently and thus carry a liquidity premium. This tends to be true of
all but the senior-most (typically Aaa-rated, floating-rate) tranches.
Thus nonsenior arbitrage CDO tranches are also good candidates
for resecuritization transactions. CDOs backed by more “exotic”
collateral, such as emerging-market debt, are particularly illiquid.

The Balance Sheet Motivation
Banks and other financial institutions may
sponsor resecuritizations — regardless of
where current spreads stand — to remove
structured securities from their balance sheets.
They do this via “balance sheet” Collateralized
Loan Obligations (CLOs). The ABS or MBS
tranches that are ripe for resecuritization would
typically be the retained portions of transactions underwritten and/or sponsored by the
banks. Here, the motivation is not to achieve
spread arbitrage, but rather to free up regulatory and economic capital or to obtain alternative funding sources.

CDOs Provide Flexibility
Until recently, the repackaging of structured
securities has been applied mainly to a single
asset class, and often to a static pool of
securities. Examples include ReRemic
(Resecuritization of Real Estate Mortgage
Investment Conduit) transactions backed by a
static pool of subordinated CMBS, or by a
static pool of RMBS.

But through the application of CDO analytics,
several multisector resecuritizations have been
completed over the past year.4 In comparison
with static, single-sector transactions, multisector CDOs facilitate diversification within the
collateral pool. In addition, like nearly all CDOs, these transactions are structured to permit reinvestment and at least a limited degree of trading flexibility, providing collateral managers with
the ability to manage credit risk and maintain leverage to enhance equity returns. Originators of
these CDOs are also able to structure liabilities with desirable characteristics such as
predictable duration.5

1 In addition to a large number of mortgage market-value transactions, Moody’s has rated the following cash-flow deals backed by structured assets
(including REIT debt): Loch Ness (ABS), Ben Nevis One (ABS), Fortress (CMBS, REIT debt), DASH I and DASH II (ABS), ZING 1 and ZING 2 (CDOs),
SABRE (ABS), Bleecker (ABS), Talon (ABS), Equinox (CDOs), Phoenix (ABS), INGRESS (ABS), MACH ONE (CMBS, REIT debt, RMBS), SFA (ABS),
PPM (ABS), Diversified REIT Trust 1999-1 and 2000-1 (REIT debt), a private CDO of CDOs, Beacon Hill (ABS), St. George Funding (diversified structured debt) and two credit default swap transactions backed by ABS.
2 A description of the type of information that is helpful in evaluating the characteristics of the collateral pool is contained in Appendix IV.
3 Some of the deals may also have some exposure to REIT debt.
4 Single-sector repackaging has also been achieved through CDOs.
5 During the reinvestment period, subject to the satisfaction of collateral guidelines, principal proceeds may be reinvested. This allows a CDO to maintain its leverage over a longer period of time. The reinvestment feature is especially useful if the collateral is likely to amortize quickly. Limited trading
flexibility is common in CDOs, allowing for more preemptive credit decisions and offering investors the opportunity to benefit from a collateral
manager’s expertise.

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Moody's Approach to Rating Multisector CDOs

The analysis of cash-flow, multisector CDOs backed by ABS, CMBS, RMBS and other CDOs,6
requires consideration of a number of issues, including:
• Diversification
• Credit quality (likelihood of default and assumed recovery rates for the collateral)
• Cash-flow characteristics
In Appendix I, we identify the various asset classes that have so far been considered for multisector CDO collateral pools. We now turn to the modeling issues that must be confronted in
rating multisector CDOs.

MEASURING DIVERSITY
Moody’s diversity score makes it possible to mimic the loss distribution of the true collateral
portfolio by representing the pool with a number of identical assets, each with independent
default risk. The reduction of the actual portfolio to a synthetic pool of identical assets in this
way facilitates the process of calculating the expected losses associated with each rated
tranche. The diversity score is the number of such identical assets. Other things equal, the
diversity score will be higher for pools in which the assets have lower default correlation, and in
which the distribution of asset size is more uniform.
For traditional CDOs, a diversity score is computed by grouping the collateral assets by
industry. For multisector CDOs, we apply a similar approach, in that the assets are grouped
into several categories or sectors. In some cases, these ABS or MBS “industries” may be at
least as independent of each other as are the corporate industries used in a traditional CDO. In
others, there is reason to believe that certain sectors are linked by more than overall macroeconomic performance, so that some correlation should be assumed between them. Both interand intra-sector default correlation should affect the value of the diversity score.7 Other collateral characteristics, including rating, maturity and size, also play important roles in this alternative computation of the diversity score. Apart from diversification by asset type, we also look for
diversification and limitations with respect to servicers and originators. Factors such as
geographic or vintage concentration may also be important.

Allocating Structured Securities to Sectors
Similar to the diversification analysis of common CDOs, the first step is to classify the collateral
pool according to asset type. Appendix I provides a list of some common structured security
types, including: auto ABS, credit card ABS, equipment leasing ABS, home equity loan ABS,
manufactured housing ABS, small business loan (SBL) ABS, student loan ABS and some more
esoteric ABS types;8 CDOs; CMBS conduits, CMBS Credit Tenant Lease (CTL) and CMBS
large loans; Residential A mortgages and residential B&C mortgages; REIT debt.
Besides the above more commonly known structured securities, we anticipate that new securitization products will continue to develop. Thus over time we will revise our asset classifications
to accommodate market innovations.9

Application of the Alternative Diversity Score Methodology
Because the interpretation of an “industry” in a CBO of structured assets differs somewhat
from that of a typical CDO, we have modified our diversity score calculation. The goal, however,
remains the same—to determine the number of independent, identical assets that mimics the
loss distribution of the actual collateral pool. The calculation of the “alternative” diversity calculation is presented in Appendix II.
6 See also “The Inclusion of Commercial Real Estate Assets in CDOs,” Moody’s Special Report, October 1999.
7 Of course, for Moody’s traditional CDO analysis, bonds in different industry categories are linked via the performance of the overall economy, but
that correlation is captured through the stressing of default rates, rather than the diversity score.
8 We also classify home equity lines of credit, sometime known as HELOC, in this category.
9 Some recent market innovations include the securitization of mutual fund fees, tax liens, structured settlements and future flows. Inclusion of these
more esoteric asset types often entails Moody’s review.

Moody's Approach to Rating Multisector CDOs

•3

Diversity for Guaranteed Instruments
Some structured securities may benefit from a guarantee, or equivalent enhancement, from a third party. These enhancements may
take the form of a financial guaranty insurance policy from monoline guarantors such as FSA, AMBAC and MBIA, guaranties by
companies active in securitizations such as Conseco and Clayton
Home, and letters of credit from banks.
Payment deficiencies in principal or interest or liquidation losses
may be supported by a guarantee. The guarantor may be required
to make deposits to an account, make advances, or purchase
defaulted collateral. The scope, amount, and allocation of payments
made under and pursuant to the guarantee will vary from transaction to transaction. The rating on the tranche supported by the
guarantee will be contingent on the maintenance of the guarantor's
credit rating.
A typical insurance policy offered by a monoline entitles security
holders to receive timely payment of interest when due, and the
payment of principal no later than the stated legal maturity. The
wrap is typically unconditional. Thus should the structured instrument become distressed, its performance will be tied to the financial strength of the guarantor. To reflect this credit enhancement
within our sector classification scheme, we include such wrapped
assets within the industry represented by the guarantor-e.g.,
“insurance” in the case of a monoline, the appropriate corporate
sector in the case of a corporate guarantee, and “banking” in the
case of a bank letter of credit.10

For the purpose of calculating the diversity score
for a pool of structured securities, multiple debt
tranches from a single transaction will usually be
consolidated as one security.11 After consolidating a collateral pool in this way, the average
rating, average maturity, and the total face value
of consolidated securities is applied for the
purpose of alternative diversity score calculation.

Assumptions about Default
Correlations
In order to apply the alternative diversity score,
we must make assumptions about default
correlations. Implicitly, any measure of diversification relies on such assumptions. Because
there have been very few defaults among structured instruments, our default assumptions are
based on a priori views as to the extent to
which different asset classes are related.
Default correlation is associated with the credit
quality of the collateral, and we factor this
assumption into our diversity score calculation.
For example, the default correlation for investment-grade ABS is lower than the default
correlation for below-investment-grade ABS.
Thus the assumed correlation for a pool of
ABS subordinated tranches would be higher
and the diversity score lower than for a pool of
senior ABS obligations.12

In addition to the impact of collateral rating levels on our correlation assumptions, we believe
that the performance of certain types of structured securities are more tightly linked than
others. For example, some of the most developed structured sectors are related in some way
to consumer finance. These include credit card, auto, home equity loan, manufactured housing
and student loan securities. Within this broad sector, which includes the bulk of ABS, we
assume that auto and credit card ABS are more highly correlated with each other than with
other ABS because they are closely related to consumer behavior. Home equity loan and
manufactured housing deals are moderately correlated with credit card and auto ABS, but
more correlated with each other. Student loan paper is modestly correlated with the other
consumer-finance oriented ABS because most student loans are either fully or partially guaranteed by the government. All of these categories are assumed to be uncorrelated with less traditional ABS types such as mutual fund fee, tax lien and structured settlement securitizations.13
Residential A mortgage deals are more highly correlated with each other than with Residential
B&C deals. Also, both Residential A mortgage and Residential B&C mortgage are moderately
correlated with home equity loan and manufactured housing deals.
10 In truth, the default behavior of the instrument will share something with other structured assets of the same type, and something with other guaranteed obligations. For consistency with the rating of the instrument, which is normally that of the guarantor, we believe is more appropriate to associate the default characteristics of the asset with that of the guarantor.
11 To the extent that the two tranches within the same transaction have very different ratings, we may depart from this practice. It is apparent that the
default of a very junior tranche within a transaction does not assure that the senior-most tranche will default (though a senior-tranche default does
indeed imply a junior-tranche default). The assumption of 100% default correlation is a simplifying assumption in cases where the rating gap is relatively narrow.
12 In addition, default correlation should be a function of collateral maturity as well. Default correlation is generally smaller over short investment horizons, but it increases over time and then should decrease with time. For empirical evidence, see “Default Correlation and Credit Analysis” by D. J.
Lucas, the Journal of Fixed Income, March 1995. For some analytical results, see “Default Correlation: An Analytical Result” by C.S. Zhou, Federal
Reserve Board working paper, 1997.
13 Echoing footnote #7, we observe that though we may assume no correlation for certain pairs of ABS sectors, they are clearly linked by overall
economic performance. However, as in a conventional high-yield CDO, that correlation is captured in our methodology through the stressing of
default and recovery rates, rather than explicit correlation assumptions (with a direct link to the diversity score calculation).

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Moody's Approach to Rating Multisector CDOs

For CDOs with both structured credits and corporate bonds included in the collateral pool, we
believe a certain degree of default correlation may exist between structured credits and corporate bonds for certain sectors. For example, the performance of a CMBS CTL security may be
linked to the default behavior of a retail firm and/or a corporate bond within the “building and
real estate” industry; or, a franchise loan deal backed by loans to fast food restaurants may be
linked to the behavior of a corporate bond within the “personal, food, and miscellaneous
service” industry. One must lay out the default correlation assumptions for each pair of credits
before applying Moody’s alternative diversification analysis.
In practice, our assumed default correlations range as high as 40%.14 The highest assumed
correlations generally apply to pairs of noninvestment-grade assets with narrowly defined
sectors. Assumed correlations for pairs of investment-grade credits would rarely surpass 15%.
Apart from the consumer finance-related ABS, and linkages between mortgage-related ABS
and RMBS, most of the structured instruments in different sectors are considered to be independent of each other.
We stress that for ABS and MBS, as for virtually all structured debt, this is more or less a theoretical view. In the absence of meaningful default data, it is impossible to develop empirical
default correlation measures based on actual observations of defaults. Our default correlation
assumptions instead reflect extensive discussions with Moody’s analysts who have expertise
with the various types of ABS and MBS, as well as a considerable degree of common sense.
For example, we have reasoned that at a given rating level, narrowly defined ABS categories,
such as consumer finance sectors, should exhibit higher correlation than typical CDO industries. To the extent that additional data relating to the potential correlation in defaults for structured tranches becomes available, we will modify our assumptions.

Geographic, Servicer and Vintage Concentration
We believe that our correlation assumptions are reasonable, as well as somewhat conservative,
provided that the collateral pool does not exhibit excessive geographic concentration. For
example, on a collateral pool look-through basis, the assumptions would not be valid if the
underlying assets within the ABS or MBS pool were all originated in a single state. As a guideline, we are comfortable applying our correlation assumptions where no more than 20% (by par
amount) of the underlying credits backing the securities are originated in a single state, with
exceptions for California, New York and Texas, where a somewhat higher ceiling would be
acceptable. The exceptions recognize that a disproportionate volume of ABS and MBS is
backed by assets from these large states, and that the economies of these states are relatively
well diversified. Excessive geographic concentration would result in a modification of our correlation assumptions.
Similarly, we would expect the pool to be reasonably well diversified across servicers. Here the
concern is a potential correlation in the performance of the assets associated with the performance of the servicer.15 In general, a badly performing or defunct servicer can be replaced, but
there may be delays or a disruption of cashflows that could result in outright pool losses in
connection with the transfer of servicing responsibility. Thus we would generally encourage
diversification of servicers, with the possible exception of very highly rated entities for which the
likelihood that a replacement will be required is remote.
For cases in which multiple securities generated by the same originator are included in one CDO,
similarity in collateral type, geographic concentration, or underwriting standards may also give rise
to default correlation. For example, seasoned issuers may execute a few deals of the same type
each year. Deals issued in the same year, and backed by a particular collateral type, may well
perform very similarly—the vintage effect. By contrast, deals issued in different years are less likely
to perform similarly. Such vintage effects may reflect a particular set of underwriting standards, the
common quality of the loans, or the competitive landscape at a particular point in time.
14 The highest figure applies to B-rated, low-diversity, cash-flow CDO tranches. CDO default correlations were inferred by simulating the default
behavior of underlying CDO pools, making realistic assumptions about industry and asset overlap between transactions. Note that correlations may
be even higher for pairs of market-value CDOs backed by similar assets.
15 Other factors that may affect deal performance include the practices of an originator, the standards of an underwriter, and the reputation of a seller.

Moody's Approach to Rating Multisector CDOs

•5

Inclusion of deals done in different years serves to mitigate the vintage effect. If multiple
tranches from the same transaction are included in a CDO, we will usually consolidate them
into one bond, effectively assuming 100% default correlation between them. For investmentgrade credits, if two bonds come from two different transactions of the same type and by a
same issuer, we assume: extremely high correlation if the two issues are sold in the same year,
very high correlation if they are sold between one and two years apart, and high correlation if
they are sold more than two years apart. For below-investment-grade credits, the corresponding correlation assumptions would be even more severe.
When CDO tranches are included in a multisector pool, factors such as the mixtures in collateral managers and ramp-up period may come into play. Deals done by the same manager may
share the same management style, such as the same credit preference, sector positioning and
trading patterns. Arbitrage CDOs that are ramped up during the same time period may share a
large number of the same names, and may be affected by the same market conditions, such
as the relative price of the underlying collateral. Consequently, these factors may lead to correlated performance of CDOs. Moody’s will adjust its default correlation assumptions to reflect
these concerns.

Global Pools Can Boost Diversity
We have, to date, focused on pools of collateral generated within the U.S. But the pace of
growth in structured finance is even more rapid in Europe and Asia than in the U.S. By
purchasing structured instruments backed by assets in a variety of countries, it may well be
possible to achieve even greater diversification. Indeed, this may be an attractive alternative to
structuring conventional high-yield CDOs — particularly in view of the still immature markets for
high-yield corporate debt in Europe and Asia.
In general, we believe that there is opportunity for significant independence between structured
asset types across different countries. Diversity increases when looking at distinct asset types
— e.g., CMBS in the U.K. vs. consumer loans in Germany — but even within a single asset
class, diversification can be achieved by pooling assets from several different countries.
Because economies outside the U.S. are generally not as well diversified as those within the
U.S., it is reasonable to assume somewhat higher default correlation for a given pair of asset
types within any single European or Asian
A Study to Gauge Recovery Rates Leads to Conservative Assumptions
country.
Because potential loss severity is an important factor in expected
loss estimations, Moody's conducted an extensive study of a wide
range of ABS, MBS and CDO transactions to ascertain the likely
extent of losses in the event of default for each transaction type.
We first sampled a large number of structured transactions over a
variety of asset classes. We then identified the risk characteristics
for typical structures within each asset class. These characteristics
included Moody's rating assumptions about collateral cash-flow,
excess spread, collateral loss distribution and so on. Next, we
applied numerous cash-flow scenarios to structured transactions
based on typical priority of payment schemes and liability structures. With this process, we were able to determine severity of loss
for each tranche in those cases where losses might occur. Based
on these scenarios, we developed somewhat conservative recovery
rate assumptions for various tranches within several types of ABS,
MBS and CDO structures, as set out in Appendix III.17

ASSESSING CREDIT QUALITY:
DEFAULT AND RECOVERY RATES
Moody’s ratings of other structured products,
like its ratings of CDOs, require an analysis of
the expected losses posed to investors in each
rated tranche. These expected losses depend
on both the likelihood of any loss for the
tranche, as well as the probable extent of loss
should there be a shortfall vis-à-vis the rated
promise to pay coupons and return principal.16
Modeling cash-flows for the limited number of
assets in a CDO pool requires judgments
regarding both the likelihood of default for each
collateral asset, as well as the ensuing
recovery rate in the event of a default.

16 Within the ABS world, the expected loss is normally expressed as a basis-point reduction from the promised internal rate of return (IRR).
Nevertheless, regardless of whether expected loss is expressed as a percentage loss of present value or a reduction in IRR, the concept is the same
— the probability-weighted average shortfall across possible scenarios with respect to a predetermined promise. Measures such as recovery rate
and severity of loss have the same interpretation for ABS as, say, CDOs.
17 To clarify the meaning of “conservative” in this context: here, lower assumed recovery rates are generally more conservative, even given the
expected loss of the ABS tranche. Intuitively, a lower recovery rate implies that each default in the pool has a greater consequence for the CDO of
structured securities. The greater effect of this “lumpiness” is akin to a lower diversity score for the pool.

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Moody's Approach to Rating Multisector CDOs

Unlike corporate bonds, defaults for structured securities have been rare, and the history of
securitization is relatively short. Consequently, for structured products, reliable empirical
evidence on default rates, rating migration history and recovery rates is not yet available.
Nevertheless, we know that structured transactions are rated to achieve consistency between
the ratings and corresponding expected loss benchmarks.
Our assumptions relating to the expected losses associated with structured tranches that serve
as assets in multisector CDOs are therefore based on our ratings. Should additional information
become available — i.e. through a meaningful number of actual defaults and recoveries on structured tranches — we will incorporate that information into our analysis.
In general, the assumed recovery rate will be higher the more highly rated the tranche, the larger
the tranche (as a percentage of total liabilities in the structure), and the smoother the distribution
of losses within the collateral pool (as, for example, in credit-card ABS, vs. emerging-market
CDO transactions). Appendix III illustrates Moody’s severity of loss assumptions.
For securities that are insured by financial guarantors or are guaranteed by corporations, losses
will only occur if both the security is in default and the guarantor becomes insolvent. Where the
guarantor is a corporation or a bank, we assume a corporate recovery. Where the guarantor is
a monoline (and thus a shadow rating is available for the guaranteed tranche), we assume the
recovery rate for the relevant instrument type.18
Once the recovery rate for a tranche has been determined, it is used in conjunction with the
expected loss implied by the rating and the weighted average life of the tranche to calculate the
assumed default rate. In this way, the default and recovery rate behavior of each collateral
asset can be modeled along with the corresponding impact on the cashflows generated by the
collateral pool.
It is important to note that our recovery rate assumptions depend on the initial capital structures of the transactions from which the instruments that comprise the resecuritization CDO’s
collateral pool are derived, as well as the initial ratings of these instruments. Both the capital
structures and the ratings may change as amortization triggers are hit, or transactions amortize
on schedule. Our study of recovery rates already anticipates that capital structures and, especially, ratings will change prior to defaults on the underlying collateral.

ASSESSING CASH-FLOW CHARACTERISTICS
In this section, we will focus on some cash-flow characteristics of multisector CDOs, including
the principal amortization profile and its relationship to the weighted average coupon, prepayment sensitivity, the weighted average life, reinvestment risk, the likelihood of a deferral of
interest and the inclusion of interest-only strips (IOs).

Amortization Profile and Weighted Average Coupon (WAC)19
In contrast to typical corporate bonds, most ABS and MBS tranches are amortizing, rather
than bullet instruments. Hence, the outstanding balances of most ABS and MBS tranches
decrease over time.
One key element in structuring a multisector CDO is the WAC of a collateral pool. However,
simply relying on the initial WAC as a modeling input is not sufficient. For example, in a staticpool, multisector CDO, if high-coupon assets amortize faster than low-coupon assets, the
WAC of collateral will fall over the life of the transaction. Or, if high-coupon assets are more
prepayment sensitive, in a declining interest rate environment, they may prepay faster than lowcoupon assets. Consequently, the WAC of the collateral pool may decline as rates fall. In either
case, the risk is that the interest cash-flow generated by the collateral pool will be insufficient to
pay the interest on the CDO liabilities.
18 We adopt this conservative approach because it is not clear how the noteholders will recover from the estate of the guarantor if the guarantor
becomes insolvent before the structured instrument defaults. For example, it is not clear how a state insurance regulator would set aside resources
for future contingent claims if, say, a monoline insurer failed. If one could be confident that such resources could be appropriately scaled and set
aside, the recovery rate for the guaranteed instrument would then be Rs + Rg * (1-Rs), where Rs is the recovery rate for the security, and Rg is the
(corporate) recovery rate for the guarantor.
19 For pools with both fixed-rate assets and floating-rate assets, the weighted average spread (WAS) should be examined in conjunction with the WAC.

Moody's Approach to Rating Multisector CDOs

•7

For the purpose of applying Moody’s CDO model,20 we must determine a WAC commensurate
with the WAC of the collateral pool. Given the pool, assuming no defaults and the base-case
prepayment speed (described below), the base-case cash flow is generated for each credit in
the pool. Ultimately, using the current pool,21 the weighted average cash-flow characteristics
can be established for each period throughout the life of the transaction.
Once the principal amortization and WAC schedules have been identified for the initial pool,
Moody’s may assume conservatively, for example, the smallest WAC across time for the
purpose of modeling CDO cash flows. On the other hand, the reinvestment flexibility that is
common to most revolving CDOs may help the collateral manager to maintain the projected
WAC around its target level. Once the manager has identified a target WAC that is consistent
with the initial portfolio, Moody’s will model the cash flows according to the target WAC, which
will also be reflected in the indenture.

Prepayment Sensitivity
Clearly, collateral cash flows are affected by both defaults and prepayments. Various collateral
default scenarios are built into Moody’s analytic approach, wherein reductions of cash flow due
to defaults are taken incrementally, one “diversity bond” at a time.22
Prepayment speeds for structured securities depend on a variety of collateral and structural
features.23 For example, the prepayment speed of the underlying collateral pool, as well as the
timing of recoveries following charge-offs, will affect the prepayment behavior of a structured
security. Structural features such as the allocation scheme for prepayment proceeds will also
affect the prepayment behavior of the structured security.
Collateral prepayment characteristics differ from one asset type to another. For our purposes, it
is useful to distinguish between structured products backed by amortizing assets, and those
backed by nonamortizing assets.
• Amortizing assets, such as fixed-rate mortgages, fixed-rate home equity loans (HEL)24 and
auto loans, have scheduled interest and principal payments. If the borrower pays more than
the scheduled payment, the extra payment is effectively a prepayment.
For residential mortgages, the borrower implicitly pays the lender a higher rate of interest for
the right to prepay at any time. By contrast, for almost all commercial mortgages, the
borrower is either prohibited from prepaying or faces significant financial disincentives to
prepayment. Prepayment protection comes in various forms, with a “lock-out,” or complete
prohibition against prepayment, being the strongest.25 In our analysis, we assume commercial mortgage loans do not prepay when the lock-out is still effective.

20 See “The Binomial Expansion Method Applied to CBO/CLO Analysis”, Moody’s Special Report, December 1996.
21 The cash flow of a structured security may depend on several factors, including the characteristics of the underlying assets, the capital structure,
interest coverage or principal coverage triggers, reserve account and/or excess spread mechanisms, and other priority of payment features. Often,
the cash flows for public ABS and MBS are available via software vendors such as Trepps, Intex and Conquest. For private issues, the coverage of
the software vendors may be less comprehensive. Under these circumstances, we will generally rely on the underwriter’s runs with confirmation from
third-party auditors.
22 Thus if the diversity score is, for example, 20, then each default within Moody’s binomial model will result in the loss of 5% of cash flows (before any
recovery).
23 Due to the range of asset types within the structured finance marketplace, a variety of measures of prepayment speed exist. Common scales include
the single month mortality rate, constant prepayment rate, Pubic Securities Association rate, absolute prepayment speed, home equity prepayment
rate, manufactured housing prepayment rate and prospectus prepayment rate.
24 Home equity loans can take two forms. The closed-end version, where the loan amount and term to maturity are known at origination and the loan is
primarily fixed rate, is more often called HEL. The open-end alternative, where the borrower receives a home equity line of credit that can be drawn
down and paid back over time and often carries a floating interest rate, is generally referred to as a HELOC. For Moody’s diversification purpose,
they are classified in one category.
25 For the purpose of prepayment stress runs for CDOs, we assume commercial mortgages prepay immediately in whole once any lock-out provision
expires. Another aspect of commercial mortgage loans is the balloon loan extension. We assume an extension of three years for balloon loans for the
purpose of CDO stress testing.

8•

Moody's Approach to Rating Multisector CDOs

• Non-amortizing assets, such as credit card receivables and home equity lines of credit
(HELOC), do not have a fixed payment schedule. The borrower has to pay a minimum
amount. Thus, there is usually no concept of “prepayment” for non-amortizing assets
because there is no predetermined amortization schedule.
The timing of cash flows from credit card ABS may be affected by many factors, including
payment and utilization rates for the underlying, and other structural features. To simplify the
CDO analysis, we use the expected life and cash flows based on average payment and
draw rates for credit card or HELOC collateral as the base case. We will use the legal final
maturity of the tranche for the purpose of stress testing.26
With the exception of some bank-balance-sheet CLOs, CDO notes generally have no
scheduled principal payments prior to the legal final maturity. Principal payments may occur
unexpectedly following a failure to meet an overcollateralization test, but such payments
would not be received in transactions that perform well. Deals that are performing well,
however, may be called after the noncall period expires. For CDOs with a revolving period,
prepayment risk from the underlying bonds is mitigated because prepayment proceeds and
collateral recoveries are reinvested in eligible collateral during the revolving period.
To simplify the analysis: for arbitrage CDOs, we will use the zero-default cash flows and the
corresponding expected weighted average life (WAL) as the base case; for master trust
balance-sheet CLOs, we will use the zero-default cash flows assuming average bank loan
payment and draw rates, and the corresponding expected WAL as the base case.27
Stressing Prepayment Sensitivity

Because the extension or compression of collateral cash flows may directly affect default likelihood, credit enhancement and excess spread for a CDO, it is important to examine the stability
of a CDO rating under different prepayment scenarios. Prepayments can be a result of turnover,
refinancings, defaults and partial paydowns. If a CDO includes amortizing assets, sensitivity
analysis is required to ensure that the ratings are robust across a range of prepayment
scenarios. To determine the base-case speed for seasoned deals, we use the actual average
prepayment speed of the past six payment periods as an estimate. For newly issued tranches,
we use the speed assumed to price the transaction. In the slower-speed case, we typically
reduce the base-case prepayment speed by 50%. In the rapid-prepayment case, we typically
double the base-case speed.
This practice of stressing the WAL and cash flow by halving or doubling prepayment speed is
intended to capture in our ratings some relatively extreme prepayment scenarios. Because the
prepayment behavior differs from one asset type to another, other stresses may be appropriate
for some collateral pools. For some asset types, such as, Residential A mortgages, prepayment speed tends to be quite sensitive to interest rate changes. In contrast, subprime mortgages may have more stable prepayment rates because subprime borrowers generally have
fewer prepayment options and often find it more costly to refinance. For auto or student loan
ABS, prepayments have little to do with interest rate changes and are generally stable. As a
rule, we will want to apply a wide range of prepayment speeds to sectors with more volatile
prepayment characteristics, but may only apply a narrow range of prepayment scenarios to
sectors with more stable prepayment patterns.
In general, provided a straight sequential waterfall, senior classes are more sensitive to collateral prepayment than junior classes because prepayments are allocated first to senior classes.
Thus, junior tranches are less prone to prepayment risk but more prone to extension risk than
senior tranches. Since it is typically the junior tranches that are resecuritized via CDOs, we
believe that halving and doubling prepayment speeds is sufficiently stressful, provided that a
CDO neither has a huge exposure to highly prepayment-sensitive securities (such as the senior
classes of Residential A mortgage securities) nor is heavily invested in extension-prone securities (such as deeply subordinated Residential A mortgage securities).
26 For stress testing purpose, notice that assuming zero payment rate may not lead to lengthening in WAL. This is because of a common structural
feature present in those deals whereby early amortization is likely to be triggered under the circumstance of extremely low prepayment rate. Thus,
the WAL may in fact be shortened.
27 For multisector pools with a large bucket in CDOs, this may be refined.

Moody's Approach to Rating Multisector CDOs

•9

Weighted Average Life (WAL)
The WAL of the CDO collateral pool is an important modeling input because it partially determines the default probability assigned to the assets.
In high-yield, leverage-loan or emerging-market CDOs, the weighted average maturity (WAM)
profile is often used for the purpose of the collateral quality tests. Because collateral assets are
generally structured with bullet principal payments, the WAM is a good proxy for the WAL. In
CDOs of structured instruments, however, most of the assets are amortizing. For this reason, a
WAL test, rather than a WAM test, is necessary. In practice, the WAL will be based on actual
prepayment speed and current underlying default experience. Any prepayment risk or extension risk should be reflected by varying the WAL in different scenarios.

Reinvestment Risk
An environment in which prepayments are particularly high is typically not the best for reinvestment. For example, Residential A securities may end up prepaying when interest rates are low.
At such times, it may be difficult to reinvest prepayment proceeds into new Residential A securities without eroding the WAC of the pool. In practice, the proceeds may be reinvested in other
sectors with good relative values as long as portfolio WAC is maintained or improved.
Within a multisector CDO, diversification across various asset classes helps to mitigate reinvestment risk. For example, CMBS prepayments may not be driven by the same factors as
Residential A security prepayments. Because of the hefty prepayment penalties that are
common in CMBS structures, fixed-rated commercial mortgage borrowers may prepay only if
the improvement in commercial property value is large enough to offset any prepayment
penalty that may be incurred.
A further means of mitigating prepayment risk is the treatment of any prepayment premiums as
principal, rather than as interest proceeds. Thus during the revolving period, such proceeds
would be used to purchase more eligible collateral; after the revolving period, the proceeds
would be used to pay down CDO liabilities.

Risk of Deferral in Interest
Disruption of cash flows in structured securities may take several forms. Deferral in scheduled
interest or scheduled principal, and pay-in-kind (PIK) notes are two examples of such disruptions.
Clearly, if a rating addresses the promise of timely payment of interest and principal, as is typically true for senior tranches in structured transactions, the risk of disruption of cash flows is
reflected in the rating. In other words, a default will result if those classes do not receive interest
payments on time. For many junior tranches, however, Moody’s ratings may not address the
promise of timely payment of interest and principal.28 In these cases, the risk of disruption of
cash flows must therefore be separately analyzed.
In CDOs backed primarily by structured securities, cash-flow disruption risk may be mitigated
by features such as write-down provisions, servicer advancing, reserve accounts, liquidity
swaps and the priority of payments within the CDO.
Write-down provisions, through which the principal balance of an ABS instrument is reduced
(or written down) to reflect losses in the collateral backing the ABS instrument, ensure current
measures of interest due on, and the principal balances of, structured securities. The CDO’s
interest-coverage and par-value tests will be adjusted for any written-down amount29 so that
they can properly reflect the status of the underlying collateral.

28 For example, we will not assign a rating of A2 or better to a CDO tranche that is PIKable. We also seek to avoid dramatic discrepancies between the
rating suggested by expected loss, and the likelihood of a payment interruption.
29 In mortgage deals, appraisal reduction amounts may be used as a preemptive signal for write-downs.

10 •

Moody's Approach to Rating Multisector CDOs

For assets that do not have explicit write-down provisions, it may be appropriate to incorporate
the concept of a “loss event.” If the outstanding collateral balance, after adjustment for defaults
— and giving effect to any excess spread and available reserves — is smaller than the sum of
the outstanding balances of the security and any other senior or pari-passu liabilities, a loss
event has occurred with respect to the security. Under such circumstances, the multisector
CDO’s interest-coverage and par-value tests should be adjusted to reflect the loss amount. For
assets that allow for PIKing, similar loss measurements should be applied. In addition, if the
tranche has been PIKing for more than a short period of time—say, six months or one-year—it
should generally be written down to the lesser of the tranche’s market value and its assumed
recovery amount. Alternatively, a rating-based definition of a loss event could be incorporated.
Servicer advancing helps to provide continuity in cash flows. Servicers will often step in to
advance funds to the transaction if the servicers believe that the advances are likely to be
repaid. Also, some deals have reserve accounts or third-party guarantees that may offer additional protection against an interest shortfall.
Two widely used mechanisms to ensure that interest continues to be paid on the multisector
CDO’s liabilities are reserves and liquidity swaps. Cash reserves may be funded at the outset,
or through the trapping of excess interest over time. Liquidity swaps ensure that interest will
continue to be paid on the liabilities (at least with a likelihood given by the swap provider’s
rating), even if there is a temporary interruption of the cash flow generated by the pool’s assets.
Finally, for structures in which interest is paid to all of the rated tranches before principal is allocated to pay the tranches, the ability to tap into the principal waterfall for interest coverage
offers strong protection against an interest shortfall. By contrast, transactions in which interest
is paid to the senior class, followed by principal to that class, and similarly down the capital
structure, there is an increased likelihood of a cash-flow disruption for the all but the senior
tranche — particularly when the senior notes are subject to a sinking fund schedule.

Inclusion of Interest-Only Securities (IOs)
Most of the multisector CDOs that we have seen to date are collateralized by investment-grade
credits. Compared to a typical high-yield or emerging-market deal, the multisector deals therefore offer less excess spread between the coupons paid on the assets and those paid on the
liabilities. To enhance the interest coverage for multisector deals, collateral managers may
include a limited basket of IOs in the collateral pools.
One of the most important considerations when including IOs in cash-flow CDOs is the stability
of the IO cash flows. The impact of prepayment risk, default risk and the allocation mechanism
for IO cash flows are of particular importance.
Most ABS and MBS do not have the reinvestment feature that is common in CDOs; hence
prepayment proceeds of the underlying assets are passed through to security holders directly.
Prepayments accelerate ABS and MBS securities, and often lead to reductions in the
outstanding notional balances of issued securities. Because an IO often represents a strip of
interest collections based on the current notional balance, this may lead to severe reduction in
IO cash flows.
As noted earlier, commercial mortgage deals typically offer greater cash-flow stability than residential mortgage transactions because of the prepayment protection provisions present in
most CMBS deals. In addition to lock-out features—complete prohibitions against prepayment
— yield maintenance provisions may also be in place. Such provisions permit prepayments, but
require the borrower to make an additional payment sufficient to maintain the investors’ yield.

Moody's Approach to Rating Multisector CDOs

• 11

To date, fixed-rate CMBS IOs and franchise loan IOs have been included in multisector cash-flow
CDOs. The main reason is that fixed-rate CMBS and franchise deals have strong prepayment
protections, while floating rate CMBS and most RMBS deals have weaker protections. Because it
is generally difficult to predict IO prepayments, the exposure of CDOs to such IOs is generally
limited to 5% of the pool, based on purchase proceeds. Furthermore, we assume commercial
mortgage and franchise loans prepay in full as soon as their prepayment protections expire.
We do not generally reflect the presence of IOs in calculations of the diversity score or the
weighted average rating factor (WARF) in multisector CDOs. Because the ratings of IOs often
only address the priority of payments, rather than the likelihood of the IO receiving timely
payment of promised cash flows, it is inappropriate to include the ratings of IOs in the WARF
calculation. Furthermore, since the IO is not associated with any payment of principal and the
present value of IO cash flows is small in comparison to those of conventional instruments, we
simply assume that IO has no contribution to CDO collateral par, and thus no contribution to
the diversity score.
For the purpose of determining the portion of cash flows from an IO that should be included in
multisector CDO cash-flow projections, the notional balance of the IO in the collateral pool is
given a “haircut.” The haircut is intended to include only the portion of the IO that represents
claims on cash flows from tranches with ratings at least as high as the average rating of the
multisector CDO’s collateral pool.
We apply such haircuts to make sure that in the cash-flow modeling of the transaction, in
which the WARF plays a key role, the IO’s credit quality will be no worse than the WARF of the
collateral pool. That is, although most IOs are rated Aaa, their credit risk may be linked to the
most subordinated certificate from which the particular IO strip is derived. As an example, if the
WARF of the pool were consistent with a rating of Baa2, and if the IO strip represented a claim
on cash flows from tranches in a CMBS deal with ratings of Aaa, Aa2, A2, Baa2 and Ba2,
the IO notional should exclude the Ba2 portion.

CONCLUSION
Resecuritization transactions now account for about 20% of the flow of new CDOs. In order to
achieve sufficient diversity for pools of structured assets, most of these transactions take the
form of multisector CDOs. Though multisector transactions raise analytical issues with respect
to the calculation of diversity score, default and recovery rate assumptions, and cash-flow
characteristics, we can express meaningful credit opinions about these CDOs by modifying our
existing analytical approach. Going forward, we anticipate that the flow of multisector CDOs will
not only continue, but that the transactions will be structured to accommodate an even wider
range of collateral.

12 •

Moody's Approach to Rating Multisector CDOs

APPENDIX I
Classification of Structured Securities
Asset-Backed Securities
Consumer finance-related instruments:
Auto (loan or lease)
Credit Card
Student Loan
Home Equity Loans/Lines of Credit
Manufactured Housing
Aircraft/Equipment Leasing
Entertainment Royalties
Small Business Loans
Tax Liens
Mutual Fund Fees
Structured Settlements
Floor Plan
Utility Stranded Cost
Health Care
Rental Car

Commercial Mortgage-Backed Securities
Conduit
Large Loan
Credit Tenant Lease

Residential Mortgage-Backed Securities
Residential A
Residential B&C

REIT Debt
Hotel
Multifamily
Office
Retail
Industrial
Healthcare
Self Storage
Diversified

Collateralized Debt Obligations
Domestic Corporate
Emerging Market

Moody's Approach to Rating Multisector CDOs

• 13

Special Considerations for Certain Asset Classifies
The intuition behind our choices of sector groupings for structured instruments should generally
be clear, but the classification of a few instruments requires further comment.
RMBS

As indicated above, we have divided Residential MBS (RMBS) into Residential A and
Residential B&C subsectors. RMBS transactions are often designated as “Jumbo-A,” “Alt-A”
(alternative-A) or “High LTV” (loan-to-value) as well. Jumbo-A loans, also known as Residential
A mortgage loans, have similar credit quality to agency mortgages, but the loans within the
pool tend to be larger. High LTV pools, provided that they contain virtually all first-lien loans,
should normally be grouped in the B&C (or subprime) mortgage bucket. Alt-A loans, in contrast
to subprime loans, are made to borrowers with good credit records, comparable to “A-” quality
loans, but the borrowers may have some trouble documenting their incomes. For the purpose
of CDO diversification analysis, we place Alt-A transactions in the Residential A bucket.
Though Home Equity Loan and Manufactured Housing transactions are classified within the
broad ABS sector, we explicitly assume some correlation between these classes and RMBS
instruments.
SBL ABS and CDOs

We have placed Small Business Loan (SBL) ABS and CDOs in different buckets, although both
transaction types are backed by corporate obligations. The small businesses in SBL obligor
pools are typically very small, unrated entities, such as gas stations, food stores, automobile
dealerships or small hotels. They tend to focus more on the local markets in which they reside,
and the performance of the SBL pools is often tied to the health of local economy. By contrast,
the obligors in most CDO pools are large, nationally or internationally oriented firms.
SBL ABS may also resemble CMBS because the pools are secured by first liens on commercial real estate. The distinction, however, is that the real estate behind an SBL is used as an
integral part of the business being financed. For example, a default by the owner of a small
food store or gas station financed by an SBL is not likely to be related to how strong the rental
market is for shopping centers or convenience stores. Unlike the loans within a CMBS pool,
however, the SBL does not rely on the rental of the property to produce cash flow. Rather, the
small business is the key for supporting the loan. The real estate is the asset of last resort if the
business fails.
Segmentation by Rating, Country

Though not explicitly indicated in the above classification scheme, we also divide each security
type into two subclasses when assigning default correlations: investment-grade and noninvestment-grade securities. Because of the very low diversity associated with CDOs of CDOs and
the consequent need for finer distinctions, we have further refined the classes into letter-rating
buckets; e.g., “B” CDO tranches, “Ba” CDO tranches, etc.
Also, additional sectors may be appropriate where the portfolio is internationally diversified. The
extent to which this is true will depend, in part, on the extent to which the default behavior of
an asset backing the multisector CDO are is determined by global, rather than local economic
factors. For example, consumer finance-related ABS in the U.S. is likely to be driven by factors
distinct from those affecting, say, French consumer finance-related ABS. However, aircraft
leasing transactions in the two countries may be affected by the same factors, suggesting
some default linkage.
Correlation with Corporate Industries

Though most multisector transactions focus exclusively on structured instruments, some have
begun to incorporate substantial buckets for conventional high-yield bonds. We consider many
of the structured finance sectors listed above to be correlated with certain corporate industries.
For example, aircraft-leasing transactions would be correlated with obligations from firms in the
Aerospace and Defense industry.

14 •

Moody's Approach to Rating Multisector CDOs

APPENDIX II
Alternative Diversity Score Methodology
To derive the diversity score for a pool of collateral assets with correlated default risk, Moody’s
has developed an alternative diversity score method.
The alternative diversity score methodology provides a general framework for analyzing CDO
collateral diversification. Provided that one can reasonably assess the default correlation
between assets and the other portfolio summary characteristics described earlier, the alternative diversity score method can then be adapted in a straightforward manner.
The derivation of the alternative diversity score is based on matching the mean and the standard deviation of the return distribution associated with the actual collateral pool.30 The final
result can be presented in the following format:
n

(1)

Diversity Score:

n

( Σ pi Fi )( Σ qi Fi )
i=1
i=1

D=

Σ Σ ρij pi qi p j q j Fi F j

Here, the actual collateral pool consists of n bonds; bond i has a face value Fi and a default
probability pi that is implied by the rating and maturity of the bond; the probability of survival for
bond i is qi = 1 - ρi. We also denote the correlation coefficient of default between bond i and
bond j as ρij. Consequently, the actual collateral pool can be replicated by D identical securities
with independent default risk in which the face value of each diversity bond is merely the
average face value of the pool (F)
n

F) /D
F = ( iΣ
=1 i
and each bond has the average default probability
n

p=

Σ pi Fi
i=1
n

Σ Fi
i=1

If all assets have the same rating, then the alternative diversity score in equation (1) can be
simplified as
n

(2)

D=

( ΣFi )

2

i=1

ΣΣρij Fi F j

In addition, if the notional balance of each asset is equal, equation (2) can be simplified further to
(3)

D=

n2
ΣΣρij

If all default correlations are the same, i.e., ρij = ρ, then equation (3) can be reduced to
(4)

D=

n
1 + (n - 1) ρ

Thus to calculate the alternative diversity score, one must specify some portfolio characteristics, including the rating profile, the maturity profile, the face amount of each asset, and the
default correlation assumptions.
30 A detailed explanation of Moody’s alternative Diversity Score method can be found in Credit Derivatives, Risk Books (1999), pp.112-113.

Moody's Approach to Rating Multisector CDOs

• 15

APPENDIX III
Moody’s Recovery Rate Assumptions
For the purpose of defining Moody’s recovery rate assumptions, we categorize multisector
securities in four distinct sectors:
Diversified Securities primarily include (1) Automobile Security; (2) Car Rental Receivable
Security; (3) Credit Card Security; (4) Student Loan Security.
Residential Securities primarily include (1) Home Equity Loan Security; (2) Manufactured
Housing Security; (3) Residential A Mortgage Security; (4) Residential B/C Mortgage Security.
Undiversified Securities primarily include (1) CMBS Conduit; (2) CMBS CTL; (3) CMBS Large
Loan; (4) Those ABS sectors not included in Diversified Securities.
CDOs include (1) High-diversity CDOs (diversity score in excess of 20); (2) Low-Diversity CDOs
(diversity score of 20 or less).
For Diversified Securities, the recovery rate is assumed as follows:

Rating of a Tranche
Tranche as % of capital structure
>70%
[70%, 10%)
<=10%

Aaa
85%
75%
70%

Aa
80%
70%
65%

A
70%
60%
55%

Baa
60%
50%
45%

Ba
50%
40%
35%

B
40%
30%
25%

Ba
45%
35%
30%
25%
15%

B
30%
25%
20%
15%
10%

Ba
45%
35%
25%
20%
10%

B
30%
25%
15%
10%
5%

For Residential Securities, the recovery rate is assumed as follows:

Rating of a Tranche
Tranche as % of capital structure
>70%
[70%, 10%)
[10%, 5%)
[5%, 2%)
<=2%

Aaa
85%
75%
65%
55%
45%

Aa
80%
70%
55%
45%
35%

A
65%
55%
45%
40%
30%

Baa
55%
45%
40%
35%
25%

For Undiversified Securities, the recovery rate is assumed as follows:

Rating of a Tranche
Tranche as % of capital structure
>70%
[70%, 10%)
[10%, 5%)
[5%, 2%)
<=2%

16 •

Aaa
85%
75%
65%
55%
45%

Aa
80%
70%
55%
45%
35%

A
65%
55%
45%
35%
25%

Baa
55%
45%
35%
30%
20%

Moody's Approach to Rating Multisector CDOs

For Low-Diversity CDOs, the recovery rate is assumed as follows:

Rating of a Tranche
Tranche as % of capital structure
>70%
[70%, 10%)
[10%, 5%)
[5%, 2%)
<=2%

Aaa
80%
70%
60%
50%
30%

Aa
75%
60%
50%
40%
25%

A
60%
55%
45%
35%
20%

Baa
50%
45%
35%
30%
15%

Ba
45%
35%
25%
20%
7%

B
30%
25%
15%
10%
4%

Ba
45%
40%
30%
25%
10%

B
30%
25%
20%
10%
5%

For High-Diversity CDOs, the recovery rate is assumed as follows:

Rating of a Tranche
Tranche as % of capital structure
>70%
[70%, 10%)
[10%, 5%)
[5%, 2%)
<=2%

Aaa
85%
75%
65%
55%
45%

Aa
80%
70%
55%
45%
35%

A
65%
60%
50%
40%
30%

Baa
55%
50%
40%
35%
25%

We recognize the limitation of relying simply on deal type and bond size as the key indicators
for determining the recovery rate assumption. As more data become available, we will update
our assumption accordingly. The impact of a particular recovery assumption is mitigated by the
fact that expected loss for the asset is preserved. Moreover, for the purpose of determining
whether overcollateralization tests are met in the multisector CDO, the par value attributed to a
defaulted asset will be haircut to the lesser of assumed recovery rate and market value of
defaulted security, as in typical high-yield CDOs.

Moody's Approach to Rating Multisector CDOs

• 17

APPENDIX IV
To facilitate the rating process, we will generally start with a review of the following information
on underlying collateral:
1. Transaction Structure: We will look at a summary of transaction structure, including rating,
sizing, seasoning, originator, servicer, geographical concentration).
2. Credit enhancement: What forms does the deal take (subordination, reserve mechanism
and any guaranty)?
3. Servicer’s role: Does it advance interest and principal? Who are the servicer, backup
servicer and master servicer?
4. Definition of event of default: Does the rating address the timely payment of interest and
principal?
5. Write-down provisions: Does the deal have a write-down provision and if so, how does it
work?
6. Summary of payment priority or waterfall.
7. Cash Flows: How are base-case cash flows derived? What are the early redemption provisions? What is the base-case prepayment speed? Is the bond callable?
8. IO’s structural features and prepayment provisions.

18 •

Moody's Approach to Rating Multisector CDOs

Moody's Approach to Rating Multisector CDOs

• 19

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or hold any securities. NO WARRANTY, EXPRESS OR IMPLIED, AS TO THE ACCURACY, TIMELINESS, COMPLETENESS, MERCHANTABILITY OR FITNESS FOR ANY PARTICULAR PURPOSE OF ANY
SUCH RATING OR OTHER OPINION OR INFORMATION IS GIVEN OR MADE BY MOODY’S IN ANY FORM OR MANNER WHATSOEVER. Each rating or other opinion must be weighed solely as one
factor in any investment decision made by or on behalf of any user of the information contained herein, and each such user must accordingly make its own study and evaluation of each security and of each
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hereby discloses that most issuers of debt securities (including corporate and municipal bonds, debentures, notes and commercial paper) and preferred stock rated by MOODY’S have, prior to
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Moody's Approach to Rating Multisector CDOs