Why does the Used Vehicle Price Index Service Level not match previous months? For example, in the previous file Nov 2017 Price Index was 109.0. The Dec 2017 version, released in January 2018, it is 113.2.
Each edition of J.D. Power’s Used Vehicle Price Index is accompanied by historical changes to values in recent time periods due to a normal calibration of underlying assumptions and parameters (such as seasonal adjustments) and minor updates to underlying data (i.e., newly received historical sales). The final edition of 2017 is accompanied by larger changes than is typical because of a small, but important, methodological change that is carried throughout the historical series.
Compared to earlier time periods, the last few years has shown a significant divergence in price behaviors between cars and light trucks. Trucks (CUVs, SUVs, pickups, etc.) exhibit different depreciation behaviors and different seasonal price variations and the magnitude of these differences have grown over time. Because of this, we have separated the portions of the index calculation that account for depreciation and seasonal price variations into a calibration for cars and a calibration for trucks. This allows for a more accurate accounting of these factors, which in turn allows for a more accurate accounting of the actual movement in prices outside of these factors.
In addition, a careful reassessment was made of the appropriate seasonal price variation assumptions in light of the reduction in observed seasonal peaks and troughs of the last two calendar years. The primary result of this assessment, as it concerns recent price movements, is a reduction in the size of price movements in the seasonally adjusted series for the Spring and Fall of 2017.
It is for these reasons that you have notice changes to the historical index values. If you have additional questions, please let us know.