Aug 20, 2025·Understanding IQ ScoresWhy did my IQ score change?
Why do IQ scores differ between tests? Learn why it's normal for intelligence test scores to vary due to measurement error, different tasks, and statistical factors like regression to the mean.
Dr. Russell T. WarneChief Scientist
Some RIOT examinees have taken intelligence tests before, and they may notice differences between their prior IQ score and their RIOT IQ score. Depending on the previous test, the score difference can be quite large. In one German study, IQ differences of 10 points or more on different tests were common—and the score differences were larger for people scoring above average. This is normal and does not indicate that either test is necessarily faulty. IQ fluctuations can occur for a variety of reasons: All psychological tests have a degree of “measurement error,” which is the amount of randomness that is part of test scores. Because RIOT IQs and IQs from other tests have some randomness in them, it is unrealistic to expect IQs from different tests (or even the same test) to be exactly the same.
Different tests contain different tasks. Although every intelligence test measures g, there is no such thing as a pure measure of g. By using verbal, spatial, speed, and other tasks to measure intelligence, every test measures some cognitive abilities that are different from general intelligence. These other abilities contribute to IQ. If the RIOT and the other test do not contain many overlapping tasks, then the mix of non-g abilities that each test measures will cause differences in IQ.
A statistical phenomenon called “regression toward the mean” can also cause score differences, especially among people with extremely high or extremely low scores. When regression toward the mean occurs, later scores are more average than earlier scores. If your previous IQ score was very high (or very low) and your RIOT IQ is more average, then you could be experiencing regression toward the mean. Regression toward the mean is a purely statistical occurrence and does not reflect actual intelligence changes.
None of these causes of score fluctuations are unique to the RIOT or intelligence tests. They occur in many types of tests and data. For example, medical tests also have some randomness in them. That is why most patients who have their cholesterol tested repeatedly receive results that are different. Likewise, task similarity occurs in other types of psychological tests (e.g., personality and mental health tests). And regression toward the mean occurs in many types of data. (Regression toward the mean was first identified when Sir Francis Galton observed in the 19th century that tall parents and short parents tended to have children whose height was more average.) These types of random fluctuations do not invalidate intelligence tests, and they do not reflect real changes in intelligence, but it is important to be aware of them.
On the other hand, there are some score changes that may not be randomly caused. If a RIOT test is taken repeatedly, then the later scores would be expected to be higher, a phenomenon called “practice effects.” A similar occurrence called “task familiarity” may happen if an examinee has taken a different intelligence test that has very similar tasks, for example, if both tests have Matrix Reasoning and Symbol Search subtests (which are common on intelligence tests). The second test’s score will probably be inflated because the test taker already understands how to approach the task and may even already know strategies for solving these problems. Practice effects and task familiarity are an issue with all intelligence tests, though test creators (including the team that created the RIOT) make efforts to reduce their influence. The RIOT team is conducting research to estimate how large practice effects are expected to be on the test, but for most intelligence tests, 5-10 points is typical, with larger score changes occurring when there is less time between examinations. Score increases from item familiarity tend to be smaller, though the magnitude depends on how familiar the examinee is with the different tasks on a test.
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AuthorDr. Russell T. WarneChief Scientist
