How precise are the measurements made by intelligence tests?
In order to answer this question it is pertinent to consider the following evidence (Jensen, 1980, 1981, 1998; Jones and Bayley, 1941; Moffitt, Caspi, Harkness and Silva, 1993; Neisser et al., 1996): a) the internal consistency of an IQ test tends to be situated between .90 and .95. The correlation between the length of the right arm and the left arm measured in a representative sample of the population tends to be .95. The reliability coefficients of measures such as blood pressure or cholesterol level are usually around .5; b) the correlation between a person s IQ assessed on two occasions with a week in between is .95.The correlation between an average person s weight measured twice on the same scales with a week s interval is 0.97; IQ measures at age 6 correlate at a value of .96 with IQ measures of the same subjects at age 12. IQ measures at age 6 correlate at a value of .86 with those of the same subjects at 18. The correlation between the height of a group of children at age 2 a
