Measuring Intelligence: Facts and Fallacies

Abstract

Measuring Intelligence: Facts and Fallacies, by David J. Bartholomew, Cambridge, UK, Cambridge University Press, 2004, 172 pp., $25.99 paperback. Professor Bartholomew acknowledges in his preface that he is venturing into a contentious field. His premise is that both sides in this battle are too much ruled by ideology to offer any honest, scientific discussion. He identifies Murray's and Herrnstein's The Bell Curve and Stephen Jay Gould's The Mismeasure of Man as the paradigmatic opposing polemics on each side of the debate about the hereditability of intelligence. He appoints himself as an impartial arbiter in this debate, explaining that this interest is in statistical rather than political correctness. He promises a balanced approach to the central questions in this field, such as the existence of inborn ethnic differences in intelligence. As I re-read Bartholomew's introduction, I reflect that it is not necessarily true that even handedness toward opposing polemics ensures veracity. Bartholomew steers clear of controversy for the first several chapters, spending much of that space describing the statistical roots of the measuring of intelligence. In appealing conversational style, with ample metaphors and some humor thrown in for good measure, Bartholomew explains factor analysis. This discussion is the basis for the explanation of the statistical strategy for approaching "g," the term for the elusive latent variable which allegedly represents true intelligence. Several chapters, in fact, are devoted to discussion of g and its statistical superiority over IQ as a measure of intelligence. Bartholomew also devotes a chapter to criticism of Gould, but presumably he nevertheless maintains neutrality, as the criticisms are only on scientific grounds. The author lambastes Gould for his conflation of factor analysis with principal components analysis, as well for Gould's overt political biases. After more than one hundred pages of statistical underpinnings, Bartholomew turns his attention to the big questions: to what extent is intelligence inherited; and, whether or not there are ethnic or racial differences in intelligence. Ironically, after several chapters devoted to establishing the statistical superiority of g over IQ, and after a chapter devoted to chiding Gould for statistical sloppiness, Bartholomew concedes that for discussion of the big questions, he must lapse back into the use of IQ. One cannot entirely blame Bartholomew for this decision; as he points out, the literature is almost entirely based on IQ rather than the inaccessible g, and "IQ and g are highly correlated" anyway. But then why spend almost the entire book defending the superiority of g only to concede that it has little to offer in this discussion? In the final chapters, Bartholomew notes that, while mean IQs have been found to be lower for American blacks than for whites, there are too many potential environmental confounders to conclude unequivocally that this difference in IQ reflects a difference in heritable intelligence. Paradoxically, the author, a self-proclaimed objective statistician, comes perilously close to dismissing the relevance of environmental confounders, citing "common sense". He states "…adhering to strict logic, it must be allowed that an environmental explanation cannot be ruled out…", but then departs from strict logic with the comment, "…any reasonable person would conclude that the odds seem heavily on a genetic explanation, given the difficulty of finding serious competitors on the environmental side." I suppose we are to infer that no reasonable person should conclude that poverty, discrimination, stress, poor nutrition, inadequate education, or inferior health care might be "serious competitors" with heredity. In his discussion of the hereditability of intelligence, Bartholomew takes care to point out that while the IQ of a person may be modified by the environment, that g, or innate intelligence, is by definition immutable at or shortly after birth. He acknowledges that this is a tautology, which implies that g must be influenced primarily by genetic influences, with lesser contributions from prenatal environmental influences. For example, he argues that to the extent IQ is modifiable by environmental factors, it deviates from g, or true innate intelligence. The foundation for this argument is that whatever g is, it reflects brain structure and intellectual performance in the purest sense. In other words, implicit in the use of this definition for g or true intelligence is the assumption that intelligence is that part of intellectual capacity which is congenital. Also implicit is that environmental influences do not enhance performance by affecting brain structure. Here, Bartholomew belies his own ignorance of current developmental neuroscience, which offers ample evidence that environment can and does have an influence on brain structure and intelligence. While the tired nature-nurture debate of psychometrics rages on, neuroscience continues to elucidate dynamic interactions between genes and the environment in determining intelligence. Inclusion of some current neuroscience would enrich this discussion and help to provide some answers. Professor Bartholomew is correct that the field could use a balanced and well-informed guide to sort out the science from the ideology. It certainly is a pity that he fails to achieve his goal with this book. Randall Phelps, M.D., Ph.D. Child Development Unit/UCLID Center Children's Hospital of Pittsburgh Pittsburgh, Pennsylvania