"Background
The Bureau of Labor Statistics (BLS) has made numerous improvements to the Consumer Price Index (CPI) over the past several decades. While these improvements make the present and future CPI more accurate, historical price index series are not adjusted to reflect the improvements. Many researchers, however, expressed an interest in having a historical research series that was measured consistently over the entire period. Accordingly, the Consumer Price Index retroactive series using current methods (R-CPI-U-RS) presents an estimate of the CPI for all Urban Consumers (CPI-U) from 1978 to the present that incorporates, when possible, most of the improvements made over that time span into the entire series.

The primary users of the R-CPI-U-RS data are researchers that use it as a valuable proxy of a historical estimate of inflation using current methods. In addition, the Census Bureau currently makes use of the index to adjust some of its income measures for changes in the cost of living. The direct adjustment of individual CPI index series makes this the most detailed and systematic estimate available of a consistent CPI series. This measure attempts to answer the question, “What would have been the measured rate of inflation from 1978 forward had the methods currently used in calculating the CPI-U been in use since 1978?”

It is important to recognize that the R-CPI-U-RS provides an annual inflation series that adjusts for specific changes in BLS methodology. The R-CPI-U-RS is of use to forecasters and other researchers in analyzing the trends and other movements in consumer inflation over the last few decades. The measure should help answer the question of the degree to which the measured rate of inflation has been affected by some of the improvements BLS has made.

Limitations
The R-CPI-U-RS has some limitations. First, most estimates are based on BLS research covering a short period of time and extrapolated to a longer period. Therefore, there is uncertainty surrounding the magnitude of the adjustments. Second, there have been several improvements in the CPI not incorporated into the R-CPI-U-RS, either because they do not represent changes in methodology, because they had negligible impacts on the CPI’s growth rate, or because it was impossible to systematically estimate the impacts of the new methods in past years. Examples include changes in imputation methods, improvements in methods for pricing hospital services, and some changes in quality adjustment procedures, such as for wireless telephone services. A list of the changes incorporated in the R-CPI-U-RS is available in an online table.

Available data
The R-CPI-U-RS presents an estimate of the CPI for all Urban Consumers (CPI-U) from 1978 to the present that incorporates most of the improvements made over that time span into the entire series. Note that many of the improvements occurred prior to 2000 and the monthly percent change in the R-CPI-U-RS is very similar to the published CPI-U for years after 2001; many of the differences prior to 1999, however, are substantial, reflecting major methodological changes such as the switch to a rental equivalence approach for shelter in 1983 and the adoption of a geometric means formula in 1999. Monthly data are published once a year in March."