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Reliability of IQ Scores over Time

By Inderbir Kaur Sandhu, Ph.D

Q: I'm a 28 year old PhD student in ecology in the USA. I took an IQ test (Wechsler variety for kids) at age 6 and my IQ score was 131. At the time I stuttered badly so the tester suggested I return after speech therapy as my ability to answer questions was compromised at the time. At age 12, I took another Wechsler and scored 144. Recently I began wondering if this score was still valid. I bought three books to test IQs and have taken several online IQ tests. On the online tests I've scored anywhere from 130 to over 150, with higher scores on tests that give you a score and THEN try to sell you something :) On the books I scored 144, 130, 135, and 145 on tests from no name "test your IQ" books and a 130 and 135 on a self-scoring mensa book. Anyway, I was wondering if my earlier scores at age 12 are the most reliable and if I should place any stock in recent scores given the wide range of scores I've received.

A: The intelligence tests available are supposed to be a guide to measure one's general level of intelligence. Different tests measure different skills. Usually standardized tests are said to be the single best predictor of one's level of intellectual capacity. Based on the Flynn's effect, our intelligence should be on the rise, which means that scores 30 years ago may not indicate at present what it was indicated then. The same scores are seen as lower today. For e.g., 2 persons had the same scores, one did the test 30 years ago; the other did the very same test in 2005. This does not mean that they both have the same levels of intelligence. In fact, due to the Flynn's effect, the one who did it 30 years ago is considered higher in terms of intellectual abilities that are tested. You may want to read about the Flynn's effect in an article I wrote sometime back.

What I am trying to say is that with practice, even an intelligence test is not foolproof. Most intelligence tests pretty much measure similar abilities, especially the ones online (the free ones!). Of course, one would score higher on a free test compared to a standardized test as the questions on such tests are quite similar, sometimes only rephrased.

It is, therefore, important to understand what remains stable and what changes in the development of intelligence. A child whose IQ score remains the same from age 6 to age 18, does not exhibit the same performance throughout that period. On the contrary, steady gains in general knowledge vocabulary, reasoning ability, etc., will surely be apparent. However, what does not change is her/his score in comparison to that of other individuals of the same age.

I strongly believe that no one should rely too heavily on IQ scores. These are mere scores which may guide one to determine strengths and weaknesses in certain areas and look into what can be done to improve oneself. As for you, I feel that you may be placing too much importance on the differences, which is all in the range of high ability. You are highly able and I'm sure you will produce a good PhD dissertation. Best of luck.


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