THE IMPACT OF RISING IQ SCORES ON THE DIAGNOSIS OF INTELLECTUAL DISABILITY

by Mitchel Fleming

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Over the years studies have shown that as a people we are growing taller, living longer, reaching sexual maturity earlier and scoring higher on IQ tests. Better nutrition, advances in health sciences and the greater availability and longer duration of education have no doubt contributed to these improvements. How far these changes in the human condition will extend is difficult to estimate. For example, the average American teenager is almost 6 inches taller now than they were a century ago. Shoe sizes are increasing by one-third of an inch every generation. For a time it was assumed that our genetic make-up would set limits to how tall we became or how long we lived. However with the increasing possibility of genetic manipulation, current natural limits are likely to be challenged. In 2000, Time Magazine estimated that over the next millennium the human lifespan might increase to 500 years. Others have calculated that if changes in rates of sexual maturation continue, on average girl will reach sexual maturity at 4 years of age by 22,040- How these and other developments will shape our future is difficult to foretell. Could we in the future have an seven-foot-tall, pre-teenage mother taking a shuttle to Mars to spend the weekend with her great, great, great, great grandparents?

Like other areas of development, human intelligence is also on the increase. James Flynn, a political scientist, has extensively documented the systematic and pervasive rise in IQ scores all over the world, since the introduction of standardised IQ tests in the early twentieth century. Using data from twenty countries, Flynn discovered that there have been IQ gains from 5 to 25 points in a single generation. Psychologists have for years been aware of what is known as the Flynn Effect, and the fact that IQ test norms become obsolete over time. In other words, people perform better and better over time on an IQ test, which results in an increase in the average IQ score by several points within a matter of years. When a test is re-standardised, which typically happens every 15–20 years, the average IQ score is reset to 100, making the test harder and ‘hiding’ the previous gains in IQ scores. It is only by comparing the differences in how people perform on old and new IQ tests that we are able to determine the extent of the rise in IQ scores over the years. If the rate of increase in intelligence, as detected by changes in IQ scores over the last century, continues—then the average person of the future will appear exceptionally able compared with people living now. Or, put another way, in the future we may appear to have been people of very limited ability compared with future generations.

Kanaya, Scullin and Ceci (2003) recently investigated whether the rise in IQ scores over the years has impacted on the diagnosis of intellectual disability. According to most criteria, the diagnosis of intellectual disability consists of sub-average intellectual functioning, usually specified as an IQ score of 70 or below, in addition to evidence of limited adaptive life skills and an onset of the condition before adulthood. Kanaya and her colleagues found that in the early 1990s the introduction of a newly revised IQ test (WISC-III) led to a significant rise in the number of children being diagnosed with an intellectual disability. This rise in the level of diagnosis occurred because the newer IQ test, the WISC-III, was on average 5.6 IQ points harder than the older WISC-R test for children who were in the mild intellectual disability and borderline IQ population. Last year the WISC-IV was launched and it will soon replace the WISC-III as probably the most widely used children’s IQ test in the world. The new WISC-IV is reported to be harder than its predecessor due to the Flynn Effect. So, we can expect to see a significant rise in the number of children being diagnosed with an intellectual disability over the next few years.

On the basis of the above, it appears that whether or not a child is diagnosed with an intellectual disability may to some extent be based on the year in which the child was tested and the test norms used, rather than his or her actual cognitive ability.

In conclusion, the impact of rising IQ scores or the Flynn Effect influences whether or not a person receives a diagnosis of intellectual disability, which in turn affects their right to access special educational services, receive benefits or possibly suffer the adverse consequences of the stigma that often accompanies such a diagnosis. Over the next few years in Ireland we can expect to see a rise in the number of children who are classified as having an intellectual disability and who will be entitled to special educational provision.