Question
How accurate is an IQ score?
Short answer
An IQ score is accurate to within a few points, not to the point. Clinical test manuals report a confidence interval, often around plus or minus 5 points at 95%, so a measured 110 is better read as roughly 105 to 115. Short or unsupervised tests have wider ranges than that.
Want your own number? The test is 25 visual puzzles, about 12 minutes, no sign-up.
Why a score has error
A test samples your performance on a limited set of items on one day. A different set of items, or the same set on a different day, would give a slightly different result. Psychologists call the typical size of that wobble the standard error of measurement, and test manuals use it to build a confidence interval. For full clinical tests the interval is often around plus or minus 5 points at 95% (Wechsler, 2008).
How to read a score as a range
| Measured score | Read as roughly |
|---|---|
| 95 | 90 to 100 |
| 110 | 105 to 115 |
| 125 | 120 to 130 |
| 130 | 125 to 135 |
This is why labels at band edges should be held lightly. A 109 and a 110 sit in different WAIS-IV bands but are, for practical purposes, the same score.
Try one · Abstract Reasoning
Which tile completes the grid?
Tap the option you think is right, or show the answer.
Show the answer
The missing tile has three outlined crosses (option 2).
How to solve it
- Start with the first column and name what changes from tile to tile.
- Every row and every column contains each shape (cross, star and triangle) exactly once.
- Every row and every column contains each number of shapes (two, three and one) exactly once.
- The fill (outline) stays the same in every tile.
- Check the rules on the second column, then apply them to the third.
- So the missing tile has three outlined crosses.
That was 1 puzzle. The full test has 25.
Why short tests are less precise
Precision grows with information. A long clinical battery asks many items across several kinds of task, so chance stumbles average out. A short test has fewer items, so each one carries more weight and a single lucky guess or slip moves the estimate further. That is not a flaw to hide. It is the reason an honest short test reports a wider range than a clinical one.
Other things that move a score
- Practice. A retest raises scores by about a quarter of a standard deviation on average (Hausknecht et al., 2007).
- Conditions. Tiredness, noise, a phone screen or an unfamiliar format can pull a score down.
- Test length. Fewer items means less information and a wider range.
For online tests specifically, read are online IQ tests accurate. For every part of a result, see how to read an IQ score.
Sources
- Wechsler, D. (2008). WAIS-IV Technical and Interpretive Manual. Pearson.
- Hausknecht, J. P., Halpert, J. A., Di Paolo, N. T., & Moriarty Gerrard, M. O. (2007). Journal of Applied Psychology, 92(2), 373-385. doi.org/10.1037/0021-9010.92.2.373