Bell Curve

The term bell curve has several meanings. One meaning is that of a statistical distribution, termed the normal distribution, which was identified by Carl Friedrich Gauss. Its shape is that of a bell. The other meaning comes from a book title.

This latter meaning of the bell curve relates to one of the most stimulating and controversial books published in the past two decades, written by Richard Herrnstein and Charles Murray, and titled The Bell Curve: Intelligence and Class Structure in American Life. This volume engendered a national conversation and even widespread debates about controversial issues, such as racial and ethnic group differences in intelligence test scores, the respective roles of nature versus nature in influencing intelligence, and the meaning of intelligence.

The primary thesis of this 845-page tome is that American society is undergoing a process of social stratification that is being determined by IQ. Herrnstein and Murray posited that there is emerging a ‘cognitive elite,’ a social group composed of highly intelligent people constituting the highest socioeconomic class, and that less intelligent people are gravitating to the lower socioeconomic classes. According to Herrnstein and Murray, a major problem with such social stratification based on IQ is that there will likely be less upward mobility for many individuals from lower socioeconomic classes, because highly intelligent individuals tend to marry highly intelligent individuals rather than less intelligent individuals.

The Bell Curve thus addressed the relationship of IQ to class structure in American life. It posited that success in life is largely based on inherited differences in cognitive ability among people. It also presented findings and commentary on the relationship between race and intelligence.

Although Herrnstein and Murray reviewed many empirical studies in their book, the most important source of data that they examined and discussed is the National Longitudinal Survey of Youth (NLSY), a longitudinal survey of American youth with a very large sample (originally 12,686 youth, ages 14–22). These youth were graduates of American high schools between 1980 and 1982. Herrnstein and Murray carefully reported on various extensive analyses of this data source in the various chapters of their book, The Bell Curve. Throughout the book, they used analyses of the NLSY data source to attack various programs of social assistance; these attacks, in turn, ignited widespread debates.

Herrnstein and Murray grounded their work on a traditional view of intelligence based on certain propositions:

• 1.
  There is a general factor of cognitive ability on which individuals differ.
• 2.
  IQ tests measure intelligence more accurately than do aptitude and achievement tests.
• 3.
  IQ tests measure what most people view to be intelligence.
• 4.
  IQ scores are relatively stable over much of human life spans.
• 5.
  IQ tests tend not to be biased against economic, ethnic, racial, or social groups.
• 6.
  IQ is substantially heritable, with 40% to 80% of the variation in IQ scores being attributable to hereditary factors.

There are numerous conclusions resulting from the extensive analyses in their work. Regarding poverty, Herrnstein and Murray concluded that IQ is a stronger predictor of poverty than is socioeconomic background. Regarding unemployment, they concluded that low IQ is a greater risk factor than either education or socioeconomic background. Regarding children born out of wedlock, they found that low IQ for a woman increases the likelihood that the woman will have an illegitimate child. Regarding welfare dependency, they determined that low IQ is a prominent predictor of the receipt of public welfare funds among women. Regarding parenting, they found that low IQ among White mothers is a strong predictor of low birthweight among children. Regarding crime, they concluded that low IQ is a risk factor for criminality.

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