The conceptually appropriate rental-equivalence measure of homeownership was not
incorporated into the CPI-W until 1985. Fortunately, the Bureau of Labor Statistics calculated
an experimental version of the Consumer Price Index for all Urban Consumers (CPI-U) that
substituted the residential rent index for the traditional—and flawed—homeownership cost
index. This experimental index, denoted the CPI-U, X-1, was calculated back to 1967. We
adjusted the CPI-W for mismeasurement of housing costs by assuming that it suffered from an
identical housing bias as the CPI-U, and used this adjusted CPI-W to estimate the overpayment
of Social Security benefits due to the homeownership bias in the CPI-W.