STATS ARTICLES 2011
Are smart kids really more likely to use drugs?
Rebecca Goldin PhD, November 22, 2011
New research reporting that a high IQ is associated with an increased likelihood of drug use is making the rounds in the news. Unfortunately, the media have neglected to put the study in the context of other information, or even to answer important questions about how strong this connection between IQ and illegal drug use is.
The latest burden of being highly intelligent is an increased likelihood of drug use, “especially among women,” according to a Medical News Today account of a new research published in Journal of Epidemiology and Community Health. The research was part of an ongoing longitudinal study tracking 8,000 British children from their birth in 1970 to see what happens to them as the decades roll by.
As the Los Angeles Times noted, the kids “with high IQs are more likely to use marijuana, cocaine, amphetamines and other illicit drugs as teenagers and adults.”
The original study found that British boys and girls both were more likely to have tried illegal drugs by age 30 if they scored high on an IQ test at ages 5 or 10. Even at age 16, higher IQ kids were more likely to have tried pot, and those who tried pot were more likely to have a higher IQ. The relationship persisted even after controlling for parent social class, significant psychological distress during adolescence and adult socioeconomic advantage.
The IQ tests were complicated; for the children at age 5, the researchers used a combination of tests, and then found a “direction” that captured just over 40 percent of the variance of the data. The tests were not traditional IQ tests, but they track reasonably well with IQ, according to the researchers. For children at age 10, the researchers used a modified version of the British Ability Scales, and also choose the “direction” with that best captured the data, in order to have one number to associate with the kids’ intelligence. They then normalized the data for both age groups so that 100 represented “average” and 15 points represented one standard deviation.
Data on about 8,000 16 year-olds were analyzed to compare high to low “intelligence” and its relationship to having ever used drugs. The number of these kids who had tried uppers, downers, LSD and heroin were so small that the researchers could not accurately assess the likelihood of such a user to have a high IQ. In contrast, approximately 0.7 percent of boys and 0.6 percent of girls had tried cocaine this age, while 7 percent of boys and 6.3 percent of girls reported having used cannabis. Those who reported cannabis (both boys and girls) were more likely to have had a high “mental ability” score at age 10 than those who did not, and the result was statistically significant. The average male normalized intelligence score at age 10 was 109.65 for kids who tried pot by age 16, and 103.86 for those who had not. For girls, the normalized score for those who had tried pot was 107.74 and those who had not was 101.42. Those who tried cocaine were also more likely to have a higher IQ, but the result was not significant. It should be noted that the results do not exempt average intelligence kids from drug use. These intelligence scores are less than one standard deviation from the norm.
By age 30, many more people had tried pot – so many, in fact, that the authors asked rather whether they had used it in the previous 12 months. The prevalence of cannabis use in the previous year was 35.4 percent for men (with a mean mental ability score of 104.65 at age 10) compared to the remaining 64.6 percent of men who had not (with an average mental ability score of 99.04). Women also saw a difference: 15.9 percent of women had used pot the previous year (mean mental ability score of 105.73). Those who had not been using pot had a mean mental score of 98.10.
While the results of cocaine use were not statistically significant for 16 year olds, by age 30, drug users were demonstrating statistically significant higher “mental abilities.” Men who had used cocaine in the past 12 months (8.6 percent) had an average score of 105.80, while those who didn’t had an average mental ability score of 101.38. Women who had used cocaine in the past 12 months (3.6 percent) had an average score of 108.10, while those who didn’t had an average mental ability score of 100.5. [Note that the reason these numbers suggest that the average “mental ability” is above 100 is due to the fact that the attrition over the years was higher for people who scored lower on the mental ability test.]
Unfortunately, the media neglected to put the study in the context of other information, or even to answer important questions about how strong this connection between IQ and illegal drug use is. First and foremost, the “high IQ” people were just the top third – they were generally not a full standard deviation from the norm. Secondly, the odds ratios were not particularly high. The odds ratio of having tried cannabis for the first tertile of intelligence compared to the third tertile of intelligence at age 5 is 1.90 for men and 3.16 for women. In other words, the odds that a man would try pot if he is of above average intelligence divided by the odds that he would try pot if he is below average intelligence is just under 2 to 1.
Women seem more vulnerable to the intelligence effect, having a higher odds ratio than men for both pot and cocaine at age 30, compared to men. However, men have a higher odds ratio for other drugs – women’s intelligence (at ages 5 and 10) does not seem to be associated with the use of the drugs ecstasy and amphetamines, whereas higher intelligence men are more likely to use these drugs than less intelligent men. That said, the important context is that the percentage of men using drugs at least once in the past 12 months is under 9 percent (except for cannabis), and under four percent (except for cannabis) for women. This is far less than, for example, the percentage of people in the first tertile of scorers on the intelligence tests (33 1/3 percent).
Context #2: Overall, people with higher IQ have many more advantages later in life. Clearly, trying illegal drugs is not affecting their overall well-being, compared to their lower-IQ counterparts. As the study itself notes,
“Children and adolescents who score higher on standard tests of intelligence have lower rates of mortality in mid to late adulthood…. [Other] studies suggest that higher child intelligence is linked to a lower likelihood of smoking, increased rates of smoking cessation, physical activity and fruit and vegetable intake in later life. High childhood IQ is also associated with socioeconomic advantage in later life (as indexed by education, occupational social class or income). These studies suggest that the skills captured by intelligence tests in childhood may influence how people manage their health, how they respond to public health messages concerning the risks and benefits of health-related behaviors (e.g., high childhood IQ has been found to predict healthy literacy in old age) and their social and economic circumstances in later life.”
Context #3: This study does not give evidence of increased abuse of or addition to illegal substances. The use or experimentation with drugs does not immediately imply that high IQ children are more likely to turn into addicts. The original study does cite evidence that high IQ is correlated to increased dependency on alcohol, however news reports did not mention the alcohol studies. If high IQ were directly correlated with addiction, the implications would be entirely different than if addiction levels were similar among both groups despite more experimentation and “trial” than lower-IQ counterparts.
Context #4: There are social influences. While news reports focused on the possibility that a desire to experiment and self-stimulate is behind the experimentation with drugs, other factors may also be at play, especially with regard to the abuse of drugs. For example, gifted children more frequently report being bored, or the subject of stigmatization, i.e., bullying. Reporting on research on the possible causes behind increased experimentation would be useful for the public to understand these social influences. Are high IQ children responding to negative reactions to their intelligence, or are high IQ children simply bored with their circumstances in life? If indeed the reasons behind the higher rate of having tried illegal drugs stems from trouble with mocking peers as children, perhaps we should identify bullying as the problem rather than high IQ.
News stories without context paint a picture of geniuses doping up for need of stimulation. The real story might be a little less glamorous and a little more varied. Parents can safely read to their children without fearing that it leads to widespread drug addiction.