Under quiz statistics>Question Breakdown, CANVAS displays a "Discrimination Index" value. But in the Item Analysis output for a given question, that number is actually the "Points Biserial" value and, as far as I can tell, the actual Discrimination Index is not calculated anywhere. I calculated it myself manually and the real Discrimination Index is very different than the "Discrimination Index" reported on CANVAS. 

Discrimination index and Point Biserial are different things with very different claculations, Yet, unless I am mistaken CANVAS is using the later but reporting it as the former. What numbers are actually being reported and how are they calculated?