Mental Retardation: It’s More Than Just IQ
Despite decades of research, mental retardation remains an amorphous concept defined not in black and white but in ever-changing shades of gray.
As recently as 40 years ago, the condition was defined primarily by IQ scores, with a cutoff of about 85.
But research and changing public perceptions have led to a more complex definition that reflects not only a person’s ability to master tests of mental acuity but also the ability to master life itself.
Although an IQ of 70--100 is normal--is often considered a rough standard of retardation, psychologists point to many people with such low test scores who are able to live independently, hold down jobs, marry and have families.
“What we try to do is look at the entire picture and consider all the mitigating variables” in deciding whether a person is mentally retarded, said psychologist Jack Naglieri of George Mason University, who said he has been involved in court cases involving convicts whose mental status was questioned. “Sometimes it’s not a simple thing to determine.”
That difficulty casts what appears to be a straightforward decision by the Supreme Court in a vastly muddier light. Experts predict that the number of such cases will increase dramatically as prisoners on death row try to stave off their fates.
The measurement of intelligence has a long and convoluted history that has been complicated by claims of racial bias in testing, the use of such tests on people with poor English skills, and controversy over the significance of test scores.
Even aside from cultural issues, measuring IQ is an inexact science. Results can be affected by a variety of factors, including which test is used, when it is given and the subject’s motivation. Even if a good test is used and the subject cooperates, there is still a significant chance that the actual IQ--as opposed to the measured IQ--is 10 points higher or lower.
Nonetheless, psychologists find the process valuable.
IQ, says psychologist Bruce Bracken of the College of William and Mary, “is the best predictor of almost all life events: academic success, military training, psychotherapy, midlife mortality, criminality.” People with high IQs receive the most education, get the best jobs, make the most money and live the longest. Those with the lowest IQs often get the short end of the stick.
A low IQ doesn’t mean that a person will necessarily become a criminal, but it is a predisposing factor. Studies have shown that the average IQ of prison inmates is about 92.
But the effects of low IQ can be offset by perseverance, dedication and other positive character traits.
Recognizing that complexity, the American Assn. on Mental Retardation defines the disorder as a significantly sub-average intellectual functioning combined with impairments in the ability to live and work independently. Furthermore, the condition must have roots in childhood.
“You don’t become mentally retarded at age 45,” said psychologist Fred Biasini of the University of Alabama at Birmingham.
According to various experts, from 2.3% to 2.5% of Americans have IQs of 70 or below, but only about half of those are classified as retarded because the rest are able to function adequately. Fewer than 0.25% have IQs below 50.
IQ is largely a result of genetics. Some researchers say that genes account for as much as 75% of an individual’s IQ, although others argue that the percentage is only about 55%.
Very low IQ is often the result of nature’s mistakes. From 20% to 30% of cases of severe mental retardation is caused by genetic abnormalities such as the chromosome aberrations associated with Down syndrome. Another 11% or so are caused by problems in childbirth such as loss of an oxygen supply to the fetus. Brain trauma after birth accounts for 3% to 12% of cases.
The causes of the rest are generally unknown.
The Supreme Court’s decision is likely to lead to large numbers of death-row occupants trying to prove that they are retarded. It is, in fact, quite easy to cheat on an IQ test--if you want to lower your score. You just give wrong answers.
“An astute psychologist will be sensitive to that,” Bracken said. But even if cheating is suspected, he added, the psychologist can’t arbitrarily raise the score. The tester will look at a variety of other factors before making a final determination.
“One of the keys is looking at a history of retardation,” Biasini said. “That should be easier to determine today. Many people with retardation in their 30s and 40s have school-based histories of special needs.”
In other words, the retarded now leave a long paper trail.
