Cracked Bell

James J. Heckman from the March 1995 issue

(Page 2 of 4)

The book fails for four main reasons. First, too much space is devoted to discussions of intrinsically irrelevant issues. Nothing central to the case for recognizing diversity in human abilities hinges on the issue of whether there is one "true ability" or whether there are multiple abilities--as common sense, much psychometric research, and the authors' own evidence indicate is the actual state of affairs. Despite this evidence, Murray and Herrnstein devote many pages to justifying a one-ability, or "g," model of human intelligence. Admitting that persons have multiple skills does not undermine the empirical case that heterogeneity in ability is an important fact of social and economic life. Indeed, acknowledging a multiplicity of skills emphasizes human diversity.

The long discussions of heredity also distract attention away from the main thrust of the argument and generate needless controversy. The authors acknowledge, as does most serious science on the matter, the difficulty of identifying separate genetic and environmental contributions to intelligence. Most scholars assign some weight to both sources, but the allocation of precise weights generates much well-deserved controversy. The authors fail to justify why it is useful to establish any particular set of weights or even a range of weights, except the special weight that assigns all credit to the genes.

This observation points to the second, more fundamental, reason why this book fails to provide an effective challenge to contemporary egalitarian social policy. One might oppose such policies on moral or ethical grounds. Instead, the authors choose an empirical approach. Yet they fail to develop the empirical case in a satisfactory or coherent manner.

Before I read this book, I thought that Murray and Herrnstein would do for policies aimed at reducing inequality what Murray did for poverty policy in Losing Ground, by documenting the failure of many social programs designed to boost the skills of the less able. Chapter 17 of their book discusses the mixed evidence on the success of early childhood interventions designed to boost IQ. By no means does the evidence they discuss rule out the possibility of boosting IQ through programs that enrich the learning environments of young children. Indeed, the authors acknowledge that there are strong indications that very intensive programs can be effective. Half-hearted interventions like Head Start are definitely not effective.

It is striking that the authors do not discuss the costs and benefits of various interventions. It is in these terms that public policy discussions regarding skill-enhancement programs are usually conducted. The authors seek to short-circuit all of the hard work required to make credible cost-benefit calculations by claiming that there is a genetic basis for skill differences.

But estimates of a genetic component of skills are irrelevant to the requisite cost-benefit analysis unless it can be established that all differences are genetic. No one, including the authors, claims that this is so. Only if all differences are genetic--and if no offsets to genetic endowments can be created by families, communities, or governments--would it be possible to use the information on the genetic contribution of skills to make the required cost-benefit analysis. In that extreme case, which no one accepts as empirically relevant, the costs of making change are infinite. Genetics and heritability determine all. Social programs cannot be effective.

Equally obvious is the point that knowing that all skill components are environmentally determined does not justify interventions. Knowing that we can teach calculus to a child with an IQ of 65 but only at an enormous cost would not justify a policy of doing so, except in the minds of zealots committed to extreme egalitarian visions. Discussions of nature versus nurture are irrelevant to practical policy discussions couched in terms of costs and benefits. An evaluation of the effectiveness of interventions is required to justify or oppose social policy designed to cope with inequality. The authors do not provide a systematic evaluation of such programs. The Bell Curve fails to present the hard information required to settle these matters on the factual grounds chosen by the authors.

This point is particularly telling for their assessment of education. The authors offer an inconsistent treatment of education throughout the book. Early on, they highlight the finding of many recent studies--that the economic return to education has increased in the past 15 years or so. The gaps between the wages of college-educated workers and less-educated workers has widened. This phenomenon has contributed to growing income inequality.

They also establish that more-able persons tend to attain higher levels of schooling. They acknowledge--and then go on to forget--that the relationship between education and ability is far from exact. In fact, throughout much of the book, they equate ability and education and implicitly assume that the economic returns to ability drive the economic returns to education.

On the empirical grounds chosen by the authors, this implicit assumption is false. Their own evidence (buried in Appendix 6), as well as a vast literature in empirical social science, clearly indicates that controlling for ability lowers but does not eliminate the return to schooling measured in terms of earnings. The evidence on this point is consistent across many studies. Controlling for their measure of ability, the returns to education sometimes fall by as much as 25 percent, but they never go to zero.

Ability and education are not the same thing, and both have economic rewards. Accounting for ability weakens but hardly eliminates the role of education in raising earnings. On average, an extra year of schooling still increases earnings by at least a substantial 6 percent to 8 percent. So there is room for social policy to eliminate earnings differentials between persons of the same ability level. Neither The Bell Curve nor the literature on schooling provides much evidence on the all-important question of the efficacy of education as a tool for equalizing the earnings of persons of different ability levels.

What little is known indicates that ability--or IQ--is not a fixed trait for the young (persons up to age 8 or so). Herrnstein noted this in IQ and the Meritocracy. Sustained high-intensity investments in the education of young children, including such parental activities as reading and responding to children, stimulate learning and further education. Good environments promote learning for young children at all levels of ability. In this sense, there is fragmentary evidence that enriched education can be a good investment even for children of low initial ability, because it stimulates cumulative learning processes and may raise ability. There is much more negative evidence for adults, where ability is a more stable trait. For low-ability adults, there is little evidence that educational investments are socially profitable.

The authors also disregard much recent empirical evidence by Richard Murnane and others that indicates the increasing returns to the measures used by Murray and Herrnstein account for only a small portion of the recent increase in the economic return to schooling. While payments for ability have increased somewhat in the past 15 years, there remains a substantial increase in the payment for education unrelated to the authors' measure of ability.

It is unfortunate that the authors disregard this important evidence. Operating on the empirical playing field chosen by Murray and Herrnstein, a die-hard interventionist could find much credible evidence to support an active social policy to eliminate skill differentials. Their implicit claim that ability drives the economic return to education, and the recent increase in the economic return to education, fails to pass empirical muster.

The third source of The Bell Curve's failure lies in the details of its analysis of the impact of ability on measured outcomes such as earnings. In their empirical research, the authors examine how well one measure of ability explains a variety of economic and social behaviors. They pit their ability measure against a measure of the socioeconomic status of persons when they were children. The authors intend this contrast to reveal the relative importance of "genes" and "environment" in accounting for behavior. Outcomes are much more sensitive to their measure of ability than to their measure of socioeconomic status. Large changes in the socioeconomic variables have weak effects on the outcome measures, while small changes in ability have large effects on the same outcome measures.