The weights used in constructing the indexes are estimates for the shares of one-unit detached properties in each state. For years in which decennial census data are available, the share from the relevant census is used. For intervening years, a state's share is the weighted average of the relevant shares in the prior and subsequent censuses, where the weights are changed by ten percentage points each year. For example, California's share of the housing stock for 1982 is calculated as 0.8 times its share in the 1980 census plus 0.2 times its share in the 1990 census. For 1983, the Pacific Division's share is 0.7 times its 1980 share plus 0.3 times its 1990 share.
For years since 2000, state shares are calculated as follows:
- For the 2001-2005 interval, shares are straight-line interpolated based on the state shares in the 2000 decennial Census and the 2005 values from the American Community Survey (ACS).
- For 2006-2016, the estimates are from the annual ACS.
- Until 2017 ACS estimates become available, shares from the 2016 ACS are used for subsequent periods.
The year-specific estimates of the state shares of U.S. detached housing stock can be accessed at https://go.usa.gov/xnhpK