The S&P/Case-Shiller home price index tracks monthly changes in the value of residential real estate in 20 metropolitan regions across the U.S. The composite indexes and the regional indexes are seen by the markets as measuring changes in existing home prices and are based on single-family home re-sales. The key composite series tracked are for the expanded 20-city composite indexes. The original series (still available) covered 10 cities. A national index is published quarterly. The indexes are based on single-family dwellings with two or more sales transactions. Condominiums and co-ops are excluded as is new construction. The data are compiled for S&P by Fiserv, Inc. The S&P/Case-Shiller Home Price Indices are published monthly on the last Tuesday of each month at 9:00 AM ET. The latest data are reported with a two-month lag. For example data released in January 2008 were for November 2007.