This is probably ridiculously simple but because I have to include the word 'negative' in my searches I'm constantly finding only posts and websites that discuss negative correlation which isn't what I'm stuck on.

Essentially, I have two variables and want to explore their correlation. As one is ordinal I'll be using Spearman's rank order correlation. The other variable was originally test scores (0-100) but they were transformed (I don't know the procedure involved; the data is supplied from a large dataset) to account for the fact that some test items were harder than others. The transformation created logits (don't understand this) where the scores are now ranging from -3 to +2.

What I'm not sure about is whether I can run a correlation using one variable that includes both positive and negative values?

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#### Best Answer

Yes, you can. Neither Spearman's rank correlation nor Pearson product-moment correlation are restricted to positive data, because Spearman's just deals with how are values ordered and Pearson's deals with distance of (products of) values to the mean and those work equally fine if values are negative. You can even add an arbitrary real number to any of your variables and it won't change any correlation. Probably you don't find results about negative data and correlation because sign of data doesn't matter and nobody writes about it.

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