The Bell Curve: Intelligence and Class Structure in American Life (41 page)

It took two of the leading criminologists of another generation, Travis Hirschi and Michael Hindelang, to resurrect the study of IQ and criminality that Sutherland had buried. In their 1977 article, “Intelligence and Delinquency: A Revisionist View,” they reviewed many studies that included IQ measures, took into account the potential artifacts, and concluded that juvenile delinquents were in fact characterized by substantially below-average levels of tested intelligence.
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Hirschi and Hindelang’s work took a while to percolate through the academy (the author of the 1982 edition of one of the textbooks quoted above continued to make no mention whatever of IQ),
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but by the end of the 1980s, most criminologists accepted not just that an IQ gap separates offenders and nonoffenders, but that the gap is genuinely a difference in average intellectual level or, as it is sometimes euphemistically called, “academic competence,” Criminology textbooks now routinely report the correlation between crime and intelligence, and although some questions of interpretation are still open, they are narrower than they used to be because the correlation itself is no longer in dispute.
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How big is the difference between criminals and the rest of us? Taking the literature as a whole, incarcerated offenders average an IQ of about 92, 8 points below the mean. The population of nonoffenders averages more than 100 points; an informed guess puts the gap between offenders and nonoffenders at about 10 points.
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More serious or more chronic offenders generally have lower scores than more casual offenders.
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The eventual relationship between IQ and repeat offending
is already presaged in IQ scores taken when the children are 4 years old.
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Not only is there a gap in IQ between offenders and nonoffenders, but a disproportionately large fraction of all crime is committed by people toward the low end of the scale of intelligence. For example, in a twenty-year longitudinal study of over 500 hundred boys in an unidentified Swedish community, 30 percent of all arrests of the men by the age of 30 were of the 6 percent with IQs below 77 (at the age of 10) and 80 percent were of those with IQs below 100.
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However, it stands to reason (and is supported by the data) that the population of offenders is short of very low-scoring persons—people whose scores are so low that they have trouble mustering the competence to commit most crimes.
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A sufficiently low IQ is, in addition, usually enough to exempt a person from criminal prosecution.
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Some critics continue to argue that offenders whose IQs we know are unrepresentative of the true criminal population; the smart ones presumably slipped through the net. Surely this is correct to some degree. If intelligence has anything to do with a person’s general competence, then it is not implausible that smart criminals get arrested less often because they pick safer crimes or because they execute their crimes more skillfully.
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But how much of a bias does this introduce into the data? Is there a population of uncaught offenders with high IQs committing large numbers of crimes? The answer seems to be no. The crimes we can trace to the millions of offenders who do pass through the criminal justice system and whose IQs are known account for much of the crime around us, particularly the serious crime. There is no evidence for any other large population of offenders, and barely enough crime left unaccounted for to permit such a population’s existence.

In the small amount of data available, the IQs of uncaught offenders are not measurably different from the ones who get caught.
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Among those who have criminal records, there is still a significant negative correlation between IQ and frequency of offending.
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Both of these kinds of evidence imply that differential arrests of people with varying IQs, assuming they exist, are a minor factor in the aggregate data.

Looking at the opposite side of the picture, those who do not commit crimes, it appears that high cognitive ability protects a person from becoming a criminal even if the other precursors are present. One study followed a sample of almost 1,500 boys born in Copenhagen, Denmark, between 1936 and 1938.
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Sons whose fathers had a prison record were almost six times as likely to have a prison record themselves (by the age of 34-36) as the sons of men who had no police record of any sort. Among these high-risk sons, the ones who had no police record at all had IQ scores one standard deviation higher than the sons who had a police record.
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The protective power of elevated intelligence also shows up in a New Zealand study. Boys and girls were divided on the basis of their behavior by the age of 5 into high and low risk for delinquency. High-risk children were more than twice as likely to become delinquent by their mid-teens as low-risk children. The high-risk boys or girls who did
not
become delinquent were the ones with the higher IQs. This was also true for the low-risk boys and girls: The nondelinquents had higher IQs than the delinquents.
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Children growing up in troubled circumstances on Kauai in the Hawaiian chain confirm the pattern. Several hundred children were followed in a longitudinal study for several decades.
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Some of the children were identified by their second birthday as being statistically “vulnerable” to behavioral disorders or delinquency. These were children suffering from two or more of the following circumstances: they were being raised in troubled or impoverished families; had alcoholic, psychologically disturbed, or unschooled (eight years or less of schooling) parents; or had experienced prenatal or perinatal physiological stress. Two-thirds of these children succumbed to delinquency or other psychological disturbances. But how about the other third, the ones who grew up without becoming delinquents or disturbed psychologically? Prominent among the protective factors were higher intellectual ability scores than the average for the vulnerable group.
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In the United States, where crime and race have become so intertwined in the public mind, it is especially instructive to focus on just whites. To
simplify matters, we also limit the NLSY sample to males. Crime is still overwhelmingly a man’s vice. Among whites in the sample, 83 percent of all persons who admitted to a criminal conviction were male.

The Rest of the Story

The statistically distinguishable personal characteristics of criminals go far beyond IQ. There is, for example, the enormous difference between the levels of male and female criminality, which cannot be explained by intellectual differences between the sexes. Accounts of the rapidly expanding literature on the psychological and biological correlates of criminality, which has become highly informative about everything from genes to early childhood precursors, may be tracked in numerous scientific journals and books.
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Probably as much could be learned about individual differences beyond intelligence that characterize the chronically unemployed, unmarried mothers, neglectful parents, and others who have been the subjects of the other chapters in Part II. But that is just surmise at this point. The necessary research has either not been done at all or has been done in only the sketchiest way.
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In the 1980 interview wave, the members of the NLSY sample were asked detailed questions about their criminal activity and their involvement with the criminal justice system. These data are known as
self-report data,
meaning that we have to go on what the respondent says. One obvious advantage of self-reports is that they presumably include information about the crimes of offenders whether or not they have been caught. Another is that they circumvent any biases in the criminal justice system, which, some people argue, contaminate official criminal statistics. But can self-report data be trusted? Criminologists have explored this question for many years, and the answer is yes, but only if the data are treated gingerly. Different racial groups have different response patterns, and these are compounded by differences between the genders.
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Other issues are discussed in the note.
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Our use of the NLSY self-report data sidesteps some of the problems by limiting the analysis to one ethnic group and one gender: white males. Given the remaining problems with self-report data, we will concentrate
in this analysis on events that are on the public record (and the respondent knows are on the public record): being stopped by the police, formal charges, and convictions. In doing so, we are following a broad finding in crime research that official contacts with the law enforcement and criminal justice system are usefully accurate reflections of the underlying level of criminal activity.
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At the end of the discussion, we show briefly that using self-report data on undetected crimes reinforces the conclusions drawn from the data on detected crimes.

The typical finding has been that between a third and a half of all juveniles are stopped by police at some time or another (a proportion that has grown over the last few decades) but that 5 to 7 percent of the population account for about half the total number of arrests.
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In the case of white males in the NLSY, 34 percent admitted having been stopped at some time by the police (for anything other than a minor traffic violation), but only 3 percent of all white males accounted for half of the self-reported “stops.”

Something similar applies as we move up the ladder of criminal severity. Only 18 percent of white males had ever formally been charged with an offense, and a little less than 3 percent of them accounted for half the charges. Only 13 percent of white males had ever been convicted of anything, and 2 percent accounted for half of the convictions. Based on these self-reports, a very small minority of white males had serious criminal records while they were in this 15 to 23 age range.

Like studies using all races, the NLSY results for white males show a regular relationship between IQ and criminality. The table below presents the average IQs of white males who had penetrated to varying levels of the criminal justice system as of the 1980 interview.
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Those who reported they had never even been stopped by the police (for anything other than a minor traffic violation) were above average in intelligence, with a mean IQ of 106, and things went downhill from there. Close to a standard deviation separated those who had never been stopped by the police from those who went to prison.

A similar pattern emerges when the criminal involvements are sorted by cognitive class, as shown in the next table. Involvement with the criminal justice system rises as IQ falls from Classes I through IV. Then we reach Class V, with IQs under 75, If we take the responses at face value, the Class Vs are stopped, charged, and convicted at lower rates than the Class IVs but are sentenced to correctional facilities at rates almost exactly the same rate. We noted earlier that people at the lowest levels of intelligence are likely to be underrepresented in criminal statistics, and so it is in the NLSY, It may be that the offenses of the Class Vs are less frequent but more serious than those of the Class IVs or that they are less competent in getting favorable treatment from the criminal justice system. The data give us no way to tell.

In addition to self-reports, the NLSY provides data on criminal behavior by noting where the person was interviewed. In all the interviews from 1979 to 1990, was the young man ever interviewed in a correctional facility? The odds shown in the table below (computed from the unrounded results) that a white male had ever been interviewed in jail
were fourteen times greater for Class V than for white males anywhere in the top quartile of IQ.