with νi independent of Xi and qi. In the data we do not observe qi but only the average of
grades (the jury grade)
The estimated hedonic price equation is therefore
(1)
where Since ui is correlated with , OLS of equation (1) leads
to biased estimates. Using the fact that individual grades are observed in Bordeaux II,8 we
can, however, determine the magnitude of the bias affecting the estimate of γ in our three
samples.9 This is shown in the appendix for the case β = 0 and Ji= J.
Table 2 reports the estimate of γ before correction for measurement errors (OLS of
equation 1) and its true value (i.e. the true impact of quality on price). The results show that
the bias is important when the average grade is used as a proxy for quality: the true impact