Standard deviation
Standard deviation (SD) measures score spread around the mean; IQ tests commonly use SD 15 (Wechsler) or SD 16 (Stanford-Binet).
Reviewed by: Scientific Review Team · Last reviewed: July 2026
On Wechsler scales, one standard deviation equals 15 IQ points. About 68% of the population falls within ±1 SD of the mean (85–115). Mensa's top-2% cutoff is often cited near IQ 130 on SD-15 scales.
Synonyms: SD
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FAQ
Why do SD values differ between tests?
Publishers choose scaling conventions. Always interpret scores using the manual for the specific instrument.
Scientific sources
- Wechsler Adult Intelligence Scale — Technical Manual.