Does the Normal Curve Accurately Model the Distribution of Intelligence?

Abstract

Like many human characteristics, intelligence is theorized to be normally distributed. However, a vocal minority of researchers and practitioners who study individuals with high intelligence have claimed that there are more people in the upper echelons of intelligence than would be expected if the normal curve accurately modeled the distribution of intelligence scores.^1,2,3,4 To verify this claim we carefully searched articles from the journal Intelligence dated 1979 to 2012, completed an academic journal search and reviewed national data sets for samples that permit this claim to be tested. To be included samples must have been (a) representative of the population that the intelligence test used was normed on, (b) not be the test’s norm sample, (c) have at least 1,000 subjects in the sample, and (d) examined subject intelligence using an intelligence test with norms that are no more than 15 years old. This search yielded one such sample used in a study by.5 Two national data sets were also identified for use in this review, the National Longitudinal Study of Youth (NLSY) and the Early Childhood Longitudinal Study (ECLS). We reviewed the information provided from these sources and determined that intelligence is indeed normally distributed.