One of the special things about the WAIS-IV IQ test is it provides norms even for people in the 85 – 90.9 age range. It’s not that hard to get a high IQ when you’re this old. If an 85-year-old scores as high as the average 25-year-old on all the core subtests of the WAIS-IV, they get a verbal reasoning IQ of 105, a perceptual reasoning IQ of 140, a processing speed IQ of 147, a working memory IQ of 119, and a full-scale IQ of 134.
However even these scores might be a massive underestimate. IQ is supposed to measure how smart you are compared to others your age. So if a 10-year-old is as smart as the average (white) American 10-year-old, his IQ is 100. By definition. If he’s smarter than 90% of American 10-year-olds, his IQ is 120. By definition.
So even though people get smarter with age, up until their 20s, and then get dumber with age, their IQs remain relatively constant, because IQ reflects your rank order among others your age.
The problem is, the WAIS-IV standardization sample excludes anyone who suffers from dementia or other illnesses that affect test performance. At first this sounds reasonable because you may want test norms to reflect the “normal” non-pathological population. But nearly half of all Americans over the age of 85 suffer from dementia!
So let’s say you are someone who has had average cognitive ability for his age for your entire life, from age 10 to 85. At age 10 your IQ will be 100, but at age 85, your IQ could drop to perhaps well below 90. Why the decline if you remain average for your age at both ages? Because at age 10, you’re compared to virtually all American 10-year-olds, while at age 85, you’re compared to the relatively brighter (on average) subset who have escaped dementia or even death.
One could argue that the elderly deserve bonus points on IQ tests to negate the fact that they are being compared to an increasingly elite reference group.
If we want the IQ to have the same meaning at age 10 that it has at age 85, then perhaps people with dementia should be included in the standardization sample, and for that matter, so should dead people. I’m not suggesting psychologists should dig up graves and administer the WAIS-IV to skeletons, but I am suggesting that they should statistically estimate how those dead people would have performed at age 85 had they not died, and include said scores in the standardization sample.