The study looked at car prices in Spain from 1990 to 2000. By adjusting for factors like age and unobservable characteristics, the researchers found that the cost of living increase due to car price changes was overestimated. Not including age effects in the analysis could lead to misleading conclusions. The Spanish Consumer Price Index may have been overestimated by around 0.1% on average during the sample period if age effects were left out. If both age effects and unobservable characteristics were excluded, this bias could increase to 0.2%. The findings provide insights into what influenced price changes in the Spanish car market.