United States. Bureau of Economic Analysis. "Gross Domestic Product, Fourth Quarter 2006 (Preliminary) : Technical Note, BEA 07-06,"
Bureau of Economic Analysis (BEA) News Releases
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https://fraser.stlouisfed.org/title/6148/item/598948/content/pdf/bea_newsreleases_20070228_technical-note, accessed on July 14, 2025.