Presents simple and direct demonstrations showing why basic measurement principles require that biases in data created by measurement error be removed. Refutes common objections to the correction for these biases. Also describes substantive psychological processes responsible for some types of measurement error. (SLD)

Although most discussions today start from the assumption that the secular rise in IQ must be environmental in origin, three reasons warrant giving the genetic phenomenon heterosis a closer look as a potential cause. First, it easily accounts for both the high heritability and low shared environmental effects seen in IQ, findings that are…