Any answer choice that is not the correct answer for a question.

The total of scores divided by the number of scores; the average score.

The value that lies in the middle of the distribution when the information is arranged in numerical order; the value that divides the distribution in half.

measures the correlation between the correct answer on an item and the total test score of a student. The point biserial identifies items that correctly discriminate between high and low groups, as defined by the test as a whole (as opposed to only the upper and lower 27% of a group).

A measure of variability; computed by determining the square root of the variance.