Why did my measured IQ drop 25 points?
May 17, 2013 2:41 PM   Subscribe

I took an IQ test as part of a therapy intake, and the number is 25 points lower than the average of the (close and consistent) results I received as a kid. Why, in practical terms, did this happen?

I looked the test up afterwards. It was the GAI portion of the WAIS-IV, though without the Information section.

Things I already know:

-That IQ results vary by environment (I was comfortable and well-rested and had no particular anxiety about the test).
-That there was a huge discrepancy between my results on the verbal and visual sections.
-That IQ score isn't actually a great indicator of intelligence and potential...
-...but that it actually is a semi-objective measure of certain cognitive abilities, and it's supposed to be fairly consistent throughout my life.

So. Why might this have happened? Is it a common pattern? Is it due to differences in how kids and adults are tested, or how their results are respectively measured? Is there statistical weirdness at the two ends of the scale that makes small discrepancies make a big difference? Would the lack of one of the usual test components skew the results?

(I know IQ can be a difficult subject around here. If you're a detractor, you should know that I pretty much agree with you. Here's the thing: my experience of depression involves a sense of mental decline, but I've always recognized that there's no objective evidence that I'm losing my ability to reason and learn. But this number seems like it is objective evidence, and so it was a very uncomfortable thing to be told while entering therapy. If I could understand how the test works, it would help me reason this out.)
posted by anonymous to Science & Nature (18 answers total) 5 users marked this as a favorite
The test and its analysis have changed quite a bit since you were a kid. So has your approach and experience with test-taking.
posted by iamkimiam at 2:44 PM on May 17, 2013

Do you take a lot of other kinds of tests these days? You don't say at what age you were previously tested, but kids are used to being formally tested a lot, all the time, and you may not have all the test-taking skill/familiarity you had at the time - even if you weren't worried about it per se.
posted by Tomorrowful at 2:45 PM on May 17, 2013

The intelligence quotient, by definition, is supposed to assess how you compare to others within your own age group (the average score typically being set to 100). Perhaps you were advanced as a child relative to other children around your age, but eventually everyone else caught up.
posted by halogen at 2:50 PM on May 17, 2013 [8 favorites]

Did you take exactly the SAME IQ test both times? (Sanford-Binet, Minnesota Multiphasic, whatever.) IQ scores vary from test to test; many use a score of 100 for a median, but not all. And yeah, the same test under different conditions would also result in variance.
posted by easily confused at 2:52 PM on May 17, 2013

I can't concentrate very well when I am depressed - it can get very bad when I am severely depressed. As in, I can't read more than a paragraph or two without losing focus, when normally I can sit and read for hours. When my mood returns to normal, my concentration returns to normal as well.

I don't know if my lack of ability to concentrate would show up on an IQ test, but I wouldn't be surprised if it did.

Also - yes, at the far end of any test, the test is less accurate. As an extreme example - if you guess on 100 four question multiple choice questions, you're probably going to get around 25 of them correct, give or take a couple. If you guess on 2 four-question multiple choice questions, statistically you are reasonably-ish likely to get 0,1 or 2 of them right (1/16 people will get both of them right) - which is the difference between a perfect score and a not-perfect score.
posted by insectosaurus at 2:53 PM on May 17, 2013 [2 favorites]

IQ is intelligence relative to age. For people with extremely high IQ's, after age 7 or so, it is not possible to accurately determine an IQ. Most IQ tests top out at about 140. In practical terms, this means a score of 140 means your IQ is at least 140. You didn't give us numbers, but I am assuming that 25 point drop didn't put you in the 70's, so I am inferring your score in childhood was pretty high.

More succinctly: You may have ceiling the test and it just does not go higher. (Last I heard, current tests have worse issues with this than some of the older tests.)
posted by Michele in California at 2:57 PM on May 17, 2013 [4 favorites]

one common reason is "regression to the mean". basically, if you had a score that was higher than average, its likely to move towards the mean upon retest. Also, see above for 1. different tests (and norms) for kids versus adults 2. more than one kind of IQ test and the scores are not 1:1 the same 3. new editions mean an 100 in 1990 may not mean the same thing a 100 would on a test today 4. measurement error 5. depression can affect IQ test performance, if profound
posted by gilsonal at 3:04 PM on May 17, 2013 [1 favorite]

A lot of the scores are based on timing: the faster you do something, the higher your score. But the timing process is subject to a degree of absolute error. If there's half a second of measurement error and your time was 60 seconds, it doesn't matter much. If there's half a second error and your time was a second and a quarter, it's a big deal.

IQ tests aren't really designed to measure people who are above normal. The best use of the tests is for people who have suffered some sort of brain damage (for instance, due to high fever, or drug overdose, or physical injury). The test measures several different aspects of cognition, and the real purpose is to look for dropouts, specific things that don't work well any more. If several of the tests come in about normal and one or two are drastically worse, then the therapist can concentrate on helping the patient with coping strategies, using what works to compensate for what no longer does.

But the higher your IQ, the more experimental error there is in the measurement process.
posted by Chocolate Pickle at 3:07 PM on May 17, 2013 [7 favorites]

Gilsonal, that's not what "regression to the mean" means. You're falling for the gambler's fallacy.
posted by Chocolate Pickle at 3:08 PM on May 17, 2013

A quick search turned up this scholarly article documenting significant cognitive and intellectual decline among people with depression (small sample). Given your subjective experience that you have lost of your sharpness, it would seem logical that at least some of this decline reflect a real change in functioning.
posted by metahawk at 3:19 PM on May 17, 2013 [1 favorite]

Chocolate pickle, that is exactly what "regression to the mean" means, and I don't think the gambler's fallacy applies to events that are statistically related (and two measurements of the same person's IQ are not independent trials).
posted by idiopath at 3:25 PM on May 17, 2013 [2 favorites]

So. Why might this have happened?

Well, all of the other answers aside, have you been challenging yourself and learning?

Kids are kind if forced to and curiosity goes a long way, whereas many adults seem to converge on being passive media grazers. I know plenty of ultra sharp while younger types who are pretty much in a permanent intellectual stupor.
posted by rr at 3:46 PM on May 17, 2013

Here's the thing: my experience of depression involves a sense of mental decline, but I've always recognized that there's no objective evidence that I'm losing my ability to reason and learn. But this number seems like it is objective evidence,

You may also have (subconsciously) fulfilled your expectations.

There have been various studies where, say, girls are given a test in math and told beforehand that boys tend to do better - and surprise, the girls don't do very well. But when they're told beforehand that the test is measuring some other, non-gender-related aspect, they do at least as well as boys.
posted by rtha at 3:47 PM on May 17, 2013 [3 favorites]

A few issues come to mind:

1) IQ tests taken before the age of 7 or so are generally less reliable because you are just at the entry point for many tests, so there are fewer items to measure your ability and therefore if you get even a few right, your score is higher. Also, the demands of the tests are less complex when you're younger, so you often see some drift downward as the demands become more complex. This may be less of an issue since you said the scores were consistent again at 10.

2) The Flynn Effect. For reasons we don't really understand, performance on tests drifts upward over time. The older a test is, the more likely people are to score slightly higher than the mean. When new versions of the tests are published, the norms are recalibrated and move back down again as a result. The version of the WAIS you took was just published in the last couple of years, while the kids' versions of the test were older, so it might be a factor.

3) The way the IQ scores are calculated have changed over time. The GAI you refer to takes out speed and working memory components, which is meant to be a purer measure of "reasoning ability." There are subtests on the test that measure these skills specifically, and these used to be included in calculations of verbal and nonverbal IQ. If these were strengths for you they would have increased your score in the past, but wouldn't have been included in the GAI here.

4) There may be some regression to the mean as mentioned above.

5) If you are depressed or having other mental or physical health issues, it definitely can depress your scores as well.
posted by goggie at 4:01 PM on May 17, 2013

I'd also really strongly recommend that you ask this question of the person who gave you the test. They will have some observations of your behavior that would help make sense of the scores. I'm also wondering why Information wasn't included in the calculation. It's not the typical way to calculate the score, and understanding the reasoning behind leaving it out would be helpful.
posted by goggie at 4:16 PM on May 17, 2013 [1 favorite]

Another thing to consider is that as standardized as these tests are, there is still a fair amount of subjectivity and heterogeneity in the way the test is administered and scored. The way that a therapist interacts with you, presents the questions, and scores your answers will vary from person to person and administration to administration.

Combined with the different tests, different norms used, and everything else everyone mentioned above makes it very not surprising that you would have a difference of 25 points between tests.
posted by whalebreath at 7:27 PM on May 17, 2013 [1 favorite]

As an anology: say you're a tall kid; in the 90% percentile. This is the equivalent of having a high IQ as a kid.

Now, say you're only a slightly tall adult. In the 80% percentile. This is the equivalent of having a middling-high IQ as an adult.

You're still taller than you were as a kid. You're still smarter than than you were as a kid.

If you're shorter/a bit dimmer than you were 2 years ago, that's a separate issue.

I would like to do more to challenge myself, but I have an active reading life, a research-heavy job, and a demanding creative regimen.

Between the reading, the research, and the creative stuff, this may be the time to do stuff which is recharging, rather than exhausting. I'd suggest something like gardening, cabinetmaking, hiking, or cooking over griding through some mammoth book of logic puzzles.

Ask your therapist for advice here.

-I don't think I've fallen into a permanent intellectual stupor.
How' many hours of exercise do you get a week?

How many hours of sleep a night?

And are you eating ok?
posted by sebastienbailard at 12:37 AM on May 18, 2013 [3 favorites]

Because of some of the reasons stated above, especially the fact that different children develop at different rates, the IQ distribution among kids is wider. In fact, a lot of traits are like this. If I recall correctly, for IQ, the standard deviation for adults is 15 points, but for children it's about 24.

A drop in the score is actually expected if you scored above average as a child.
posted by grahamsletter at 3:27 AM on May 18, 2013 [1 favorite]

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