Discussion

Item difficulty index can be found by dividing the number of the test takers correctly answering each item by .........

Answer: D

Divide by The total number taking the test.

The item difficulty index is the proportion of test takers who answer an item correctly:

\[ p = \frac{R}{N} \]

where R is the number answering the item correctly and N the total number taking the test.

A p of 0.9 means a very easy item, and 0.2 a hard one.

Dividing by the number of girls or boys alone gives a wrong proportion, and dividing by the number of questions mixes up items and people.

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