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rkruskal-wallis
Sinval
Sinval

Reputation: 1417

How to obtain the exact p-value of a Kruskal-Wallis test in R?

How to obtain the exact p-value of a Kruskal-Wallis (e.g. with 3 groups) test in R?

Example of data:

df <- data.frame(
    dv = c(0.80, 0.83, 1.89, 1.04, 1.45, 1.38, 1.91, 1.64, 0.73, 1.46,
           1.15, 0.88, 0.90, 0.74, 1.21),
    group = factor(rep(c("A", "B", "C"), c(5, 5, 5))))

I tried the coin package using the function kruskal_test

kruskal_test(dv ~ group, data = df,distribution= "exact")

Although an error is produced:

Error in .local(object, ...) : ‘object’ is not a two-sample problem

If I change the "exact" for "approximate" it runs, but it is not the exact distribution...

Any thoughts?

Upvotes: 0

Views: 1018

Answers (1)

Ian Campbell
Ian Campbell

Reputation: 24790

The reason you're getting the error is because you can only exactly calculate the distribtution for a two-sample problem.

From help("kruskal_test"):

...the distribution can be approximated via Monte Carlo resampling or computed exactly for univariate two-sample problems by setting distribution to "approximate" or "exact" respectively.

Upvotes: 1

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