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Is it possible to include a blocking variable with unequal sample sizes for nonparametric tests?


Community Trekker


Aug 13, 2014

Hello everyone, I am interested in using the Kruskal-Wallis test to compare several different categories. I have data from two years, and I would like to block on year to incorporate this variation. However, I do not have equal sample sizes from both years. Is it possible to block on year in JMP (or any other software) if you have unequal sample sizes for nonparametric tests? JMP tells me 'blocking was ignored because cell counts were unequal'. Is there a workaround for this?



Community Manager


Jun 23, 2011

There's no real workaround to allow for the unequal cell counts in Fit Y by X.


An alternative analysis for your situation is to save the ranks, using averages for ties from the Distribution platform. Then use Fit Model with the Rank as your Y and your categories and year as effects. It's not exactly the same as the Kruskal-Wallis but some statisticians would recognize this as a valid alternative.


Hope that helps.