By TheStreet Staff What Is the Case-Shiller Home Price Index?The Case-Shiller Home Price Index, officially known as the S&P CoreLogic Case-Shiller U.S. National Home Price Index, is a key monthly measure on the changes in value of existing single-family homes in the U.S. Its subindexes track home values in major metropolitan housing markets across the country. Unlike other indexes that focus on new-home sales, the Case-Shiller index targets existing home sales because homes often change hands, and their value can be evaluated over a long period through recorded transactions that can span decad…