Housing price models can be estimated with time-series as well as cross-sectional data. If you study aggregate time-series housing prices, you have: N 38 (annual 1970-2007) where: Pt the nominal median price of new single-family houses in the United States in year t Yt ? the U.S. GDP in year t (billions of current $) a. Carefully interpret the economic meaning of the estimated coefficients.