This table presents processed quiz data in a way suitable for anayzing and judging the performance of each question for the function of assessment. The statistical parameters used are calculated as explained by classical test theory (ref. 1)
Facility Index (% Correct)
This is a measure of how easy or difficult is a question for quiz-takers.
It is calculated as:
Standard Deviation (SD)
This parameter measures the spread of answers in the response population. If all users answers the same, then SD=0. SD is calculated as the statistical stadard deviation for the sample of fractional scores (achieved/maximum) at each particular question.
Discrimination Index (DI)
This provides a rough indicator of the performance of each item to separate proficient
vs. less-proficient users. This parameter is calculated by first dividing learners into thirds
based on the overall score in the quiz. Then the average score at the analyzed item is calculated for
the groups of top and bottom performers, and the average scored substracted. The matematical expression is:
This parameter can take values between +1 and -1. If the index goes below 0.0 it means that more of the weaker learners got the item right than the stronger learners. Such items should be discarded as worthless. In fact, they reduce the accuracy of the overall score for the quiz.
Discrimination Coefficient (DC)
This is another measure of the separating power of the item to distinguish proficient from weak learners.
Again, this parameter can take values between +1 and -1. Positive values indicate items that
do discriminate proficient learners, whereas negative indices mark items that are answered best by
those with lowest grades. Items with negative DC are answered incorrectly by the seasoned learners
and thus they are actually a penalty against the most proficient learners. Those items should be avoided.