Vol. 2, No. 2 , 1996, Page 4&5


Low IQ is a known risk factor for crime and delinquency (See related article, Crime Times, Vol. 1, No. 3, Page 6). But a new study by Robert Goodman suggests that even when IQs are in the normal range, lower IQ scores are linked to stealing, lying, and other symptoms of conduct disorder.

Goodman studied 339 children between the ages of 5 and 16. All of the children were seen at a psychiatric clinic. Children with diagnoses of hyperactivity, psychosis, pervasive developmental disorders, or retardation were excluded.

Tests revealed, Goodman says, that lower IQ in his sample of "normal-IQ" subjects was linked to conduct disorder, a link which was stronger in teens than in younger children. "Other dimensional measures of psychopathology--covering emotional symptoms, developmental immaturity and relationship difficulties--were not significantly correlated with IQ," he says.

In Goodman's sample, the mean IQ of children with conduct disorders was nearly 10 points lower than that of children with emotional disorders--and children with mixed disorders of conduct and emotion fell in between. The low-IQ subjects did not appear to be more immature or hyperactive, but Goodman says this is probably because children with overt hyperactivity were excluded from the study.

"When taken together with the results of previous clinical and epidemiological studies," he says, "the findings of this study suggest that IQ variation within the normal range does influence the risk of common childhood psychopathology." The IQ effect remained true when Goodman controlled for socioeconomic status and for reading ability, which he says indicates that "the link between low IQ and conduct problems was not wholly attributable to social class or entirely mediated by scholastic attainments.

"Given the overlap between teenage conduct disorder and juvenile delinquency," Goodman says, "it is worth emphasizing that the link in the current study between low IQ and more conduct problems was greater in teenagers than younger children. In younger children, IQ may be more closely linked to hyperactivity than to conduct problems."

Reversing low IQ?

Goodman notes that "cynics may well argue that IQ is not a very profitable risk factor to study since we have limited power to modify it." He argues, however, that "studying the mediating factors linking low IQ to more conduct problems may provide useful leads for both treatment and prevention."

Goodman suggests programs to improve the self-esteem of lower-IQ children. A growing body of research, however, suggests that more direct approaches, aimed at actually improving IQ, may be effective.

One approach is to identify and treat children suffering from elevated lead levels (See related article in Crime Times, Vol. 2, No. 2, Page 1). ). A 1993 study by Holly Ruff and colleagues found that over a six-month period, the IQs of children treated for moderate lead toxicity rose an average of 1 point for every decrease in blood lead level of 0.14 micromol. per liter.

In addition, a number of researchers report that simply improving the diets of lower-IQ children can improve their intelligence scores. Among the studies:

--In 1991, Stephen Schoenthaler and colleagues tested the effects of vitamin/mineral supplements on 26 subjects at a juvenile treatment center. After a 13-week double-blind, placebo-controlled trial, Schoenthaler found that "the group of 15 subjects on supplements produced significantly larger gains in non-verbal IQ than the group of 11 subjects on placebos."

In another study, Schoenthaler tested the effects of vitamin/mineral supplementation on 615 school children. Treated subjects in this study showed an average nonverbal IQ gain of four points.

--In a study reported in The Lancet in 1988, David Benton and Gwilym Roberts supplemented the diets of 30 school children, while giving placebos to 30 others (and no tablets at all to another group of 30). After eight months, the nonverbal IQ scores of the treated subjects had increased significantly, while the nonverbal IQs of untreated children were unchanged. Benton and Roberts noted that nonverbal IQ is more changeable than verbal IQ. "Inadequate nutrition," they said, "would be expected to show its earliest effects on the more biological intelligence measured by the nonverbal intelligence test." A 1991 study by Benton and Richard Cook, of 47 six-year-olds, produced similar results: the IQ scores of children taking the supplements increased by 7.6 points, while the placebo group's scores fell by an average of 1.7 points.

--A 1990 study by Alan Lucas, also published in The Lancet, reported that premature babies fed a special formula with extra vitamins and minerals performed significantly better than babies fed regular formula when both groups' motor, social, and mental skills (skills that correlate with later IQ) were tested at 18 months.

These and other studies suggest that dietary improvements, treatments to reduce toxic lead levels, and similar interventions can cause small to moderate gains in IQ. And Goodman's findings suggest that even small gains might make a major dent in the rate of aberrant behavior, delinquency, and crime. ).


"The relationship between normal variation in IQ and common childhood psychopathology: a clinical study," Robert Goodman, European Child and Adolescent Psychiatry, Vol. 4, No. 3, July 1995. Address: Robert Goodman, Department of Child and Adolescent Psychiatry, Institute of Psychiatry, De Crespigny Park, London SE5 8AF, U.K.


"Declining blood lead levels and cognitive changes in moderately lead-poisoned children," Holly Ruff, Polly Bijur, Morri Markowitz, Yeou-Cheng Ma, and John Rosen, Journal of the American Medical Association, Vol. 269, No. 13, April 7, 1993.


"Controlled trial of vitamin-mineral supplementation: effects on intelligence and performance," Steven Schoenthaler, S. P. Amos, H. J. Eysenck, E. Peritz, and J. Yudkin, Person. Individ. Diff., Vol. 12, No. 4, 1991; and "Controlled trial of vitamin-mineral supplementation on intelligence and brain function," S. Schoenthaler, S. Amos, W. Doraz, M. A. Kelly, and J. Wakefield, Person. Individ. Diff., Vol.12, No. 4, 1991. Address for both: Steven Schoenthaler, California State University, Stanislaus, Dept. of Sociology and Criminal Justice, 801 W. Monte Vista Ave., Turlock, CA 95380.


"Effect of vitamin and mineral supplementation on intelligence of a sample of schoolchildren," David Benton and Gwilym Roberts, The Lancet, January 23, 1988; and "Vitamin and mineral supplements improve the intelligence scores and concentration of six-year-old children," David Benton and Richard Cook, Person. Individ. Diff., Vol. 12, No. 11, 1991.


"Early diet in preterm babies and developmental status at 18 months," Alan Lucas et al., The Lancet, June 23, 1990.

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