Structural and Temporal Changes in the Housing Market and Hedonic Housing Price Indices
An economic indicator faces two requirements. It should be timely reported and should not significantly be altered afterward to avoid erroneous messages. At the same time they should reflect changing market conditions constantly and appropriately. These requirements are particularly challenging for housing price indices, since housing markets are subject to large temporal/seasonal changes and occasional structural changes. In this study we estimate a hedonic price index of previously-owned condominiums of Tokyo 23 Wards from 1986 through 2006, taking account of seasonal sample selection biases and structural changes in a way it enables us to report the indexes timely which are not subject to change after reporting. Specifically, we propose an overlapping-period hedonic model (OPHM), in which a hedonic price index is calculated every month based on data in the “window” of a year ending this month (this month and previous eleven months). We also estimate hedonic housing price indexes under alternative assumptions: (i) no structural change (“structurally restricted”) and (ii) different structure for every month (“structurally unrestricted”). Results suggest that the structure of the housing market, including seasonality, changes over time, and these changes occur continuously over time. It is also demonstrated that structurally restricted indices that do not account for structural changes involve a large time lag compared with indices that do account for structural changes during periods with significant price fluctuations.
Japan, the United States, and most advanced nations have experienced housing bubbles and subsequent collapses of the bubbles in succession. Recently, much attention has been focused on housing price indices. In macroeconomic policy, housing price indices are considered to be a possible candidate of “early warning signals” of sometimes devastating financial bubbles. In microeconomic spheres, there are growing needs for hedging against volatility in housing markets, and housing price indices may be used as a means of index trades.