# Different Shapiro-Wilk test results in R, JASP and SPSS?

Hi everyone,

I know this isn't strictly speaking a Bayes question but it's a JASP question.

I've run the Shapiro-Wilk test on the same data in all three platforms and SPSS gives me W=.789, p=.027; R gives me W=.766, p=.008 and JASP gives me W=.804, p=.022.

What should I do here?

Is there any objective reason as to why this should be the case?

## Comments

JASP uses an R package for this, must be the settings that make the difference. I'll ask Johnny to look into this.

Thank you. I was mildly confused by SPSS and R differing but I expected JASP to be the exact same as R because I knew it 'runs on R'.

This is for my thesis. How do I know which one of them to report? I've got some cases where one of them shows S-W as significant and in others it doesn't..

We'll look into it. If you are really eager, you can inspect the JASP code on GitHub and see what arguments to the R function we call. I'm inclined to trust R over SPSS, but that's a general prior value judgement.

I was using R to begin with and my analyses currently are based on the R Shapiro-Wilk tests. Was using them to determine which inferential stats to use. So I'll report the R ones for now but please do let me know what happens with the difference between JASP and R.

Hi,

I just looked into this, and JASP uses the shapiro.test() function in R. For the two-sample t-test, JASP does this separately for each group, so you get two Shapiro statistics and p-values. It might be the case that you calculated the aggregated Shapiro statistic across the two groups, leading to a different value. So for instance, for the kitchen rolls example dataset in JASP:

If you repeat this with the one sample t-test in JASP, you get the first result, and if you run the Shapiro test with the two sample t-test in JASP, you get the latter two results. I do not have access to SPSS, so I'm not sure what they do with the test.

In case this is not the reason for the differing results, could you please include a data example and R-code used to calculate the Shaprio statistics?

Kind regards,

Johnny