Joseph Kambeitz
2009-Mar-19 10:00 UTC
[R] correlation with ties & multiple comparisons problem
Hello! I am currently working on a big data set. There are different subjects that have been measured in about 40 different variables (in this case a measure of brain metabolism). Now I want to look at possbile significant correlations between those variables. As some of the variables are not normally distributed I used "spearman" as method in the function rcor.test from the ltm-package. Unfourtunatly this results in more than 50 warnings like this due to ties: In cor.test.default(mat[, index[i, 1]], mat[, index[i, ... : Cannot compute exact p-value with ties I have now two question: 1. Is there any way to calculate a exact p-value for data that is not noramlly distributed? 2. Do have to correct for multiple comparisons in this case as I am practically testing each possible pair of the 40 variables? Many thanks for your help!
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