What does the point biserial measure ?

The relationship between two variables, a categorical variable (i.e., the student either answered the test item correctly or incorrectly), with a continuous variable(i.e., percent score on the examination).

How do you interpret a point biserial correlation?

As with all correlation indices, the point biserial ranges from –1.00 to +1.00.

A positive point biserial tells us that those scoring higher on

the exam were more likely to have better item “discriminates” between high-scoring and low-scoring students).

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Item Discrimination Index

Point BIserial Correlation( rpbs )