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).
Item Discrimination Index
Point BIserial Correlation( rpbs )