Confidence Intervals on Your IQ Score
Every IQ score should be reported with a confidence interval, because every measurement has error. A clinical IQ score is typically reported as 'X ± Y at the 95% confidence level', where Y is roughly twice the standard error of measurement. For the WAIS-IV that is about ±5 points; for a brief online screener it is closer to ±10.
Every IQ score should be reported with a confidence interval, because every measurement has error. A clinical IQ score is typically reported as 'X ± Y at the 95% confidence level', where Y is roughly twice the standard error of measurement. For the WAIS-IV that is about ±5 points; for a brief online screener it is closer to ±10.
Interpreting cognitive ability scores responsibly requires understanding both the measurement and the construct. A score is a number; an interpretation is a sentence about what that number means in the context of the test, the test-taker, and the question being asked. The same score can support very different interpretations depending on those contexts.
The biggest interpretive errors made by users of online IQ tests are over-precision and over-generalization. Over-precision treats a single screener score as though it were a clinical-grade measurement: 'I scored 117, which means I am exactly at the 87th percentile of cognitive ability'. The reality is closer to 'somewhere in the upper portion of the average-to-high-average range, with measurement error of roughly ±10 points'. Over-generalization treats a single subtest score as though it characterized overall cognitive ability: 'I'm bad at math, so I must have a low IQ'. The reality is that subtest scores reflect partly distinct abilities, and the full-scale IQ is a weighted average across them.
Most useful score interpretations include three elements: the band the score falls in (extremely low through very superior), the percentile rank in the appropriate norming population, and a confidence interval that reflects the standard error of measurement. With these three elements, the test-taker has a defensible basis for self-knowledge or further assessment.
On Confidence Intervals on Your IQ Score specifically, the published research provides clear interpretive guidance. The principles outlined above apply: read the score in context, attend to the standard error, and recognize that the score reflects a sample of cognitive performance rather than an immutable trait.
If your screener result raises clinical concerns — for example, a score that is substantially below your everyday functioning, or a profile of subtest scores with unusually large gaps — consult a licensed clinician. A formal evaluation will use a battery with much higher reliability than any online screener can provide.