The quiz item analysis report provides a break down of how multiple choice questions were answered and the total attempts on the multiple choice question. For each multiple choice question the quiz item analysis report calculates the correct factor (Cor. Fac.), standard deviation (Std. Dev.), the discrimination index (Disc. Indx.), and the discriminative efficiency (Disc. Eff.).
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Calculations
% (Percentage)
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The discrimination index is performance indicator for a question which determines how well a question differentiates between high and low performers. In the Quiz Analysis report the discrimination index is represented as a percentage. The discrimination index will range from 100% to -100%. The closer the discrimination index is to 100% the more the question distinguishes between the high and low performers, and the further away from 100% the less discriminating the question is between low and high performers. A negative discrimination index indicates that the question is being answered correctly by more of the lower performers than the higher performers. A question with very good discrimination will have a discrimination index between 40-100%.
Discrimination Efficiency
The discrimination efficiency provides an additional statistic that may be used to better interpret a question’s discrimination index. The measurement attempts to assess how good the discrimination index is relative to the question’s difficulty.
The weakness with the discriminative index is that if the percentage of learners who answered the question correctly is close to 0% or 100%, meaning that a majority of the learners answered the question incorrectly or correctly, the discrimination index will always be small. The discrimination efficiency expresses the discrimination index as a fraction of the maximum possible value it could have taken given the scores the learners earned on the question and the entire test.