Mixed parametric and non-parametric tests within same study — is this valid?
Mixed parametric and non-parametric tests within same study — is this valid?
Hi r/statistics (or r/AskStatistics),
I'm writing up a psychology thesis and have a methods question I'd love some input on.
I'm comparing two conditions (problem-focused vs solution-focused news) on seven emotion ratings using independent samples t-tests. For each variable I checked normality with Shapiro-Wilk and homogeneity of variance with Levene's, and applied the following decision rule consistently across all seven emotions:
Normal distribution + equal variances → Student's t
Normal distribution + unequal variances → Welch's t
Non-normal distribution → Mann-Whitney U
This means most emotions were analysed with t-tests/Welch's, but two (Joy and Calm) were analysed with Mann-Whitney due to significant Shapiro-Wilk results.
My question is: is it valid to report these side by side in the same results table, and can I meaningfully compare the pattern of findings across emotions even though they used different tests? I'm not directly comparing effect sizes across tests (Cohen's d vs rank-biserial r) but I am drawing general conclusions about which emotions showed larger vs smaller differences between conditions.
Any input appreciated!