I am looking at the absolute difference in values between pairs of numbers. I am then comparing these absolute values between two groups (e.g. Males and Females). Since these are absolute values I am not sure whether it is appropriate to use parametric statistics (e.g. Independent t-test) or whether it is better to be using non-parametric tests (i.e. Mann-Whitney U)?
Specifically I am worried that being absolute values (created by ignoring the signs) they cannot fit the assumption of normality needed?
The largest sample size I'm looking at is 19 in Group 1 and 17 in Group 2 (however there are also some smaller groups).
Any help would be appreciated (and explanations why would be great, as I'm trying to wrap my head around all this). Thanks!