Stanines

Stanine (STAndard NINE) is a method of scaling test scores on a nine-point standard scale with a mean of five (5) and a standard deviation of two (2).

Some web sources attribute stanines to the U.S. Air Force during World War II. The earliest known use of Stanines was by the U.S. Air Force in 1943.

Test scores are scaled to stanine scores using the following algorithm:
 * 1) Rank results from lowest to highest
 * 2) Give the lowest 4% a stanine of 1, the next 7% a stanine of 2, etc., according to the following table:

The underlying basis for obtaining stanines is that a normal distribution is divided into nine intervals, each of which has a width of one half of a standard deviation excluding the first and last. The mean lies approximately in 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.