Practice effects in IQ-style tests
Take a reasoning test twice and your second score is likely to be higher. That improvement is real, but it doesn't necessarily mean your underlying ability has changed.
About five points, then less
Practice effects are score gains that occur when people retake the same or similar cognitive tests. The meta-analysis by Scharfen, Peters and Holling put numbers on this: the average gain from a first to a second administration was about a third of a standard deviation, which on an IQ scale is roughly five points. The gain from the second to the third test was about half that, and from the third to the fourth it was negligible. Causes include familiarity with the format, learned strategies, reduced anxiety and memory for specific items.
Why scores rise on retesting
| Cause | Mechanism | Changes underlying ability? |
|---|---|---|
| Format familiarity | Less time spent understanding instructions | No |
| Strategy learning | Better approaches to item types | Partly task-specific |
| Item memory | Remembering specific questions | No |
| Reduced anxiety | More attention available | No |
| Genuine learning | Improved reasoning skills | Possibly, but hard to separate |
What the second attempt is really measuring
When a test is taken for the first time, some performance goes into learning how the test works. On a second attempt, that effort is freed for solving items. Because professional assessments are designed to be interpreted relative to first-time test takers, practice effects can inflate scores. This is why formal retesting usually involves waiting periods and alternate forms, and why psychometric guidance stresses standardized conditions.
Interpreting a higher retest score
| Situation | Likely interpretation |
|---|---|
| Same online test within days | Mostly familiarity and memory |
| Similar test after practice | Strategy and format gains |
| Formal retest after a long interval with alternate forms | More informative, still includes some practice effect |
| Gains mainly on speeded items | Faster processing of familiar formats |
One case
Someone scores 105 on an online reasoning test, practices similar puzzles for a week and scores 110 on a retake. That five-point move is close to the average first-to-second retest gain in the meta-analysis, so the most likely explanation is format learning rather than a change in reasoning ability.
Using practice effects wisely
- Compare scores only across similar conditions and test forms.
- Treat the first attempt as the less-practiced baseline.
- Expect diminishing gains after the first few attempts.
Practice effect questions
What is a practice effect?+−
A score gain from retaking a test, due to familiarity, strategy or memory.
How much do IQ scores improve with practice?+−
Meta-analytic estimates are around five IQ points from the first to the second test, with smaller gains after that.
Does practice raise real intelligence?+−
Practice mainly improves performance on the tested formats.
How long should I wait before retaking a test?+−
Longer intervals reduce memory effects; formal tests often specify minimum gaps.
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