Glossary
Reliability
Definition
Reliability is how consistent a test is. A reliable test gives the same person a similar score if they take it again, and its parts agree with each other. It is usually reported as a coefficient from 0 to 1, where values closer to 1 mean less random error.
Want your own number? The test is 25 visual puzzles, about 12 minutes, no sign-up.
Why it matters for IQ scores
Reliability decides how much you can trust a single score. Clinical manuals publish reliability and standard error tables, and use them to report a confidence interval around the full-scale IQ, often around plus or minus 5 points at 95% (Wechsler, 2008). A less reliable test needs a wider range to say the same thing honestly.
Kinds of reliability
- Test-retest: does the same person score similarly a few weeks later?
- Internal consistency: do the items within the test agree with each other?
- Alternate forms: do two versions of the test give similar results?
An example
Retest scores are not a perfect check, because people improve with familiarity. Retaking cognitive ability tests raises scores by about a quarter of a standard deviation on average, roughly 4 IQ points, and more when the same form is reused (Hausknecht et al., 2007). A test-retest study has to separate that practice effect from random error.
Common confusions
Reliability is about consistency, not correctness. That second question is validity. See also standard error of measurement, and for what to look for in an online test, read how online IQ tests work.
Try one · Spatial Reasoning
Which option is the same shape, only rotated?
Tap the option you think is right, or show the answer.
Show the answer
Option 3 is the original figure turned a quarter turn counterclockwise.
How to solve it
- Pick a landmark: the marked cell or the end of the longest arm.
- Turn the figure in your head and watch where that landmark goes, and which side the other cells end up on.
- Turning the figure a quarter turn counterclockwise gives option 3.
- Each of the other options is a mirror image: flipping it over would match, but no turn does.
That was 1 puzzle. The full test has 25.
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