Definition: Item discrimination point biserial is a correlative statistic that tells you how much success on a particular question relates to the student’s success on the test as a whole. Higher discrimination means that the students that get this question correct are the ones most likely to score higher on the test. A lower discrimination means that it does not specifically predict success on test if students get that question correct.
The point biserial ranges from a low of -1.0 to a high of +1.0. The closer the point biserial is to +1.0 the more reliable the question is considered because it discriminates well among students who did well on the test overall and those who did not.
How to Find: Within the assessment dashboard, select the course (if applicable) and assessment that you would like to evaluate. On the “View by” filter, select “Questions.”You will see the bar charts of performance percentage and can download those as a CSV file. There is a little gear icon next to the “Download CSV file.” Click on this and add the column titled “Point Biserial” to your CSV download.
Note: This data can also be found on the Item Analysis tab located on the Exam Statistics report. Click here to learn how to download the Exam Statistics report.
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