Stanine

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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 1-9 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 tendency 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.[citation needed]

Calculation[edit]

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:
Calculating Stanines
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.

Use today[edit]

Today stanines are mostly used in educational assessment.[citation needed]

See also[edit]

References[edit]

  1. ^ Thorndike, R. L. (1982). Applied Psychometrics. Boston, MA: Houghton Mifflin
  2. ^ "Understanding Stanines", nzcersupport.org.nz