Item-total correlation

Under the discriminatory power of an item is understood in the classical test theory, the correlation of the item with the overall result of a test.

The selectivity to enable an assessment of how well an item separates between people with low and high characteristic value. To this end, the correlative relation of individual items is determined by the total test. For the determination of the selectivity i.d.R. a "part -whole- correction " is made, that is, the item is set to the determined from all the other items of the test value in relationship.

: Values ​​for the item i

Values ​​for the total test without the item i

The range of the selectivity is between -1 and 1 case of a high positive selectivity of the item assesses something similar to the overall test. A selectivity close to 0 indicates that an item with the rest of the test has little in common. A negative selectivity may be an indication that an item is inversely understood as intended or was not correctly polarized in the evaluation.

Rule of thumb for item selection: the items should have at least better discriminatory power than 0.30.

Swell

  • Hermann -Josef Fisseni: Textbook of psychological assessment. 3rd revised and expanded edition. Hogrefe, Göttingen 2004, ISBN 3-8017-1756-9, pp. 36-40.
  • Descriptive Statistics
  • Psychological Assessment
  • Multivariate Statistics
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