What is Stanine?
Also called Standard nine
A stanine is a standardised score on a nine-point scale with a mean of 5 and a standard deviation of 2. The name contracts 'standard nine'. Each stanine covers a fixed slice of the normal distribution, so it reports a person's position deliberately coarsely — in nine bands rather than a hundred percentile points.
The fixed slices
Stanine 1 covers the bottom 4% of the distribution, then 7%, 12%, 17%, 20% for stanine 5 in the middle, then 17%, 12%, 7%, and 4% for stanine 9 at the top. The scale was developed by United States Army Air Forces psychologists during the Second World War, where a single-digit score was a practical advantage.
The coarseness is the design, not a limitation. Nine bands are close to what a typical instrument's measurement error can actually support, and reporting in stanines makes it awkward to claim a distinction between two candidates that the test cannot sustain.
Where it misleads
The bands are unequal in width, so a one-stanine difference means different things in different parts of the scale, and the boundaries are hard: a person a fraction of a point below a boundary is reported a whole stanine lower than someone a fraction above.
Report the underlying standard score alongside the stanine wherever a decision sits near a boundary, and never compute an average of stanines across scales.
Stanine to z-score
- z = (stanine − 5) ÷ 2
- Stanine 7 → z = (7 − 5) ÷ 2 = +1.0, roughly the 84th percentile
- Stanine 3 → z = (3 − 5) ÷ 2 = −1.0, roughly the 16th percentile
Not the same as sten score
A sten is a ten-point scale with a mean of 5.5 and a standard deviation of 2, common in personality questionnaires. A stanine has nine points and a mean of 5. The names are one letter apart and the scales are not interchangeable.
Related terms
More terms beginning with S
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