“…However, when measurement error is not classical and the data exhibits mean reversion (σ X Ã , b 0) then the IV estimator will be biased upward. As Black et al (2000) notes, the IV coefficients may therefore serve as an upper bound of the true coefficient when there is non-classical measurement error. 16 As a result, in the presence of non-classical measurement error having a valid instrument does not result in an unbiased estimate of the true population regression coefficient if the mean reversion is strong.…”