Deriving an index of the difficulty of the average item for his math test

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A developer is interested in deriving an index of the difficulty of the average item for his
math test. As his consultant on test development, you advise him that this index could be
obtained bv:

A developer is interested in deriving an index of the difficulty of the average item for his math test. As his consultant on test development, you advise him that this index could be obtained by:

A developer is interested in deriving an index of the difficulty of the average item for his math test. As his consultant on test development, you advise him that this index could be obtained by: Averaging the item-difficulty indices for all test items and then dividing by the total number of items on the test.