Lindsey Austin, a master student (I guess) who works for a professor to be something (I am not sure whether she is a TA). Her professor requests her to analyze some records to see student's study ability. However, she is not good at statsitics, so she sent the data set to me.
The question is very easy: how to calculate the correlation between individual scores and GPA in reading, math, science, and fundamentals in some courses. The individual score variable is scale (0~100), but the GPA is ordinal (A+, A, A-,...., F).
In correlation analysis, there are three correlation coefficients we often use: Pearson, Kendall's tau, and Spearman. However, none of them are for the case of "scale vs ordinal".
I am wondering whether there are some special correlation coefficients that I don't know. I went to check SAS menu to see "PROC CORR", but there is no special correlation. My supervisor, Mark, even took his old handouts (because he also graduates from biostatics department in UNC-CH) to search for any evidence, but there is no way as well.
Finally, we conclude that, we can rank the individual score variable, and use Spearman correlation.
This is a pretty special case. I think there should be a specific correlation for this situation, but we haven't figure it out. If so, I will show here.
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