I'm trying to find a test to establish the correlation between a certain value of a substance measured inside the skin (continuous: 0,65 or 1,15 etc.) and the bacterial load found on the skin (ordinal: Negative, load 1, load 2, load 3, load 4)
Which test is most suited to do this?
My suggestion is to use a Spearman’s rank-order correlation (for example see here ), so that the continuous variable will be re-expressed as a ranked variable (so for each observation you will take its ordinal rank compared to the rest of the observations in the sample) and its rank will be comparable to the rank of the ordinal variable. However make sure to express the ordinal variable correctly in numerical terms. For example use 0,1,2,3 etc. Because all the variables used must be numerical.
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