Evening Must-Read: James Heckman (1995): Cracked Bell

study of racial and ethnic differentials in socioeconomic outcomes…. Evidence that racial differentials weaken when ability is controlled for using regression methods does not rule out an important role for the environment…. In the presence of measurement error in the environment, the authors’ analysis will overstate the ‘true’ effect of ability on those outcomes. There are methods for addressing these problems, but Murray and Herrnstein do not use them….

By its very construction… the ‘two-standard deviation’ range in measured IQ… [covers] 95 percent of the population. A ‘two-standard deviation’ range of their family background index does not include 95 percent of the population, because that measure does not come from a bell curve…. By restricting the range of the environmental variable they understate the role of the environment in affecting outcomes relative to the role allocated to IQ…