Each middle stanine spans 7.5 IQ points
Stanine 5 is centred on the mean (z −0.25 to +0.25). Each step out adds half an SD; stanines 1 and 9 take everything beyond ±1.75 SD.
Descriptive labels as commonly used on UK school reports (e.g. CAT4-style); wording varies by publisher.
How a typical class would spread out
If a class were a random draw from the national norm group, this is the expected count in each stanine. Real classes are not random: selective schools bunch at the top, and small groups wander far from the expected split.
Seven points can look identical; one point can look like a jump
Compare two pupils. Near a band edge, measurement error (a few IQ points on any test) is enough to flip a stanine either way. Read a stanine as "about here", and look at the underlying score before acting on a one-band change.
A wartime shortcut that stayed in schools
The US Army Air Forces' official history records that aircrew test scores "were converted into stanines", a word coined from STAndard NINE. The aviation psychology programme, headed by John C. Flanagan from 1941, combined test batteries into separate pilot, navigator and bombardier stanines. From 2 July 1942 navigator trainees needed a navigator stanine of 5 or more; from 28 November 1942 pilots and bombardiers needed at least 3, and the minimums were raised as training pipelines filled in late 1943.
The popular story that one digit was chosen to fit a single punched-card column is plausible but undocumented; Robert Thorndike argued the coarse scale was useful because it discourages reading meaning into small score differences.
After the war, test publishers adopted the scale for school reports, where it remains common in the UK, Ireland, Scandinavia and New Zealand.
Stens ("standard ten", mean 5.5, SD 2) have no middle band: 5 and 6 straddle the mean. They are used on personality inventories such as the 16PF.
- Craven, W. F., & Cate, J. L. (Eds.) (1955). The Army Air Forces in World War II, Vol. VI: Men and Planes, ch. 16. University of Chicago Press. Stanine definition and 1942 minimums.
- Flanagan, J. C. (Ed.) (1948). The Aviation Psychology Program in the Army Air Forces (AAF Aviation Psychology Program Research Reports, No. 1). US Government Printing Office.
- Canfield, A. A. (1951). The 'sten' scale: A modified C-scale. Educational and Psychological Measurement, 11(2), 295–297.
- GL Assessment. CAT4 (Cognitive Abilities Test, 4th ed.) score interpretation guidance: standard age scores, stanines and national percentile ranks.
- Cattell, R. B., Eber, H. W., & Tatsuoka, M. M. (1970). Handbook for the Sixteen Personality Factor Questionnaire. IPAT.