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THE FEUTEX TOOLKIT

Exam Item Group Discrimination

Compare a question’s correct-response rates in two equal-sized score groups.

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02 Your result
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FormulaUpper rate = 100*upper_correct/group_size; Lower rate = 100*lower_correct/group_size; Discrimination = (upper_correct-lower_correct)/group_size; Combined difficulty = 100*(upper_correct+lower_correct)/(2*group_size)

Worked example

Inputs

Group size
20 students/group
Upper correct
17 students
Lower correct
8 students

Expected results

Upper rate
85 %
Lower rate
40 %
Discrimination
0.45 index
Combined difficulty
62.5 % correct

Load the example in the workspace to reproduce these results. Display rounding does not change the underlying calculation.

How to use this tool

  1. Enter the measured quantities and your own planning assumptions.
  2. Review all calculated outputs and the stated limitations.

Try this example

{
  "group_size": 20,
  "upper_correct": 17,
  "lower_correct": 8
}

Accuracy and scope

Descriptive upper-minus-lower index for equal groups. Does not establish test validity, statistical significance or a recommended cutoff.

Is my data uploaded?

This tool runs locally in your browser. Input and output are not sent to a processing server. Copy or download your result before leaving the page.