Hi,
so I want to compare two dependent variables that do not meet the criteria for t-test because Shapiro-Wilk test is sigificant in both cases. I ran a t-test nonetheless in order to be able to get Wilcoxon W. When ticking the "normality test" box, jamovi suddenly showed me a non-significant result (it looks like both variables were somehow merged because they are not shown individually). Can someone explain me how this is possible?
Kind regards.
Test of Normality suddenly not significant?
Re: Test of Normality suddenly not significant?
hi,
provide us with a data set, and the steps to reproduce what you describe, and we'll be able to provide some insight.
cheers
jonathon
provide us with a data set, and the steps to reproduce what you describe, and we'll be able to provide some insight.
cheers
jonathon
Re: Test of Normality suddenly not significant?
This is because you ran a Shapiro-Wilk on both variables. A paired t-test is specifically interested in the difference in each pair of scores, and so the singular (non-significant) Shapiro-Wilk is actually testing the distribution of these differences - which is an assumption of this particular paired t-test.
To demonstrate this - create a new computed variable based on a simple 'Variable1 - Variable2' calculation. This will give you the difference in the pair of scores for each participant - then you can run a Shapiro-Wilk on this new 'differences' variable. It should give you the same SW and p-value you found when doing this as part of the paired t-test options!
To demonstrate this - create a new computed variable based on a simple 'Variable1 - Variable2' calculation. This will give you the difference in the pair of scores for each participant - then you can run a Shapiro-Wilk on this new 'differences' variable. It should give you the same SW and p-value you found when doing this as part of the paired t-test options!
Re: Test of Normality suddenly not significant?
Thank you very much! Fortunately, I found out the answer shortly after posting - but I still very much appreciate your help. Have a nice day!Bobafett wrote:This is because you ran a Shapiro-Wilk on both variables. A paired t-test is specifically interested in the difference in each pair of scores, and so the singular (non-significant) Shapiro-Wilk is actually testing the distribution of these differences - which is an assumption of this particular paired t-test.
To demonstrate this - create a new computed variable based on a simple 'Variable1 - Variable2' calculation. This will give you the difference in the pair of scores for each participant - then you can run a Shapiro-Wilk on this new 'differences' variable. It should give you the same SW and p-value you found when doing this as part of the paired t-test options!