Stanine (STAndard NINE) is a method of scaling test scores on a nine-point standard scale with a mean of five and a standard deviation of two.
Some web sources attribute stanines to the U.S. Army Air Forces during World War II. Psychometric legend has it that a 0-9 scale was used because of the compactness of recording the score as a single digit but Thorndike [1] claims that by reducing scores to just nine values, stanines "reduce the tendancy to try to interpret small score differences (p. 131)". The earliest known use of Stanines was by the U.S. Army Air Forces in 1943.
Test scores are scaled to stanine scores using the following algorithm:
| Result Ranking | 4% | 7% | 12% | 17% | 20% | 17% | 12% | 7% | 4% |
| Stanine | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |
| Standard score | below -1.75 | -1.75 to -1.25 | -1.25 to -.75 | -.75 to -.25 | -.25 to +.25 | +.25 to +.75 | +.75 to +1.25 | +1.25 to +1.75 | above +1.75 |
The underlying basis for obtaining stanines is that a normal distribution is divided into nine intervals, each of which has a width of 0.5 standard deviations excluding the first and last, which are just the remainder (the tails of the distribution). The mean lies at the centre of the fifth interval.
Stanines can be used to convert any test score into a single digit number. This was valuable when paper punch cards were the standard method of storing this kind of information. However, because all stanines are integers, two scores in a single stanine are sometimes further apart than two scores in adjacent stanines. This reduces their value.
Today stanines are mostly used in educational assessment. The University of Alberta in Edmonton, Canada used the stanine system until 2003, when it switched to a 4-point scale [1]. In the United States, the Educational Records Bureau (they administer the "ERBs") reports test scores as stanines and percentiles.