Point-biserial correlation when some of the test assumptions is violated




I originally posted my question on StacExchange-CrossValidated, but no one there seems to be able to answer my question.

This is the situation: I've got 15 raters who assess if there is deep invasion of a cancer type or not (dichotomous), and they can be either accurate or inaccurate. I've also asked raters how certain they are in their assessment, using a Visual Analogue Scale from 0-100.

I would like to check for an association between these variables, answering the question "Do raters know when they are accurate/inaccurate?" so that I later can see if more experienced raters are more knowing of their limitations than inexperienced raters, who can be expected to be more hit-and-miss without knowing it.

I've learned from other forums with researchers asking the same question that point-biserial correlation seems to be the way to go. Although, some assumptions are violated; I get a significant Shapiro-Wilk for some raters and a significant Lavenes test for some others and so forth.


All help is greatly appreciated!

//Rasmus Green, MD., PhD student, Karolinska Institute, Sweden