This all pertains to my Psychology honours thesis.
I have two groups (Autism and control) and all participants completed four tasks. It is very important to my study that the groups do not differ on reaction time in each of the tasks. However, they do. The autism group responded faster than the control group. This confounds the results for the construct we actually want to investigate.
I thought I might correct the difference by excluding outliers from the study. I tried to identify outliers at both the univariate (Boxplots, SD = +/- 2.5, for each of the four tasks) and multivariate level (Mahalanobis Dsq). No participant comes up as an outlier. Then I thought I would exclude participants that have low average reaction times ('low' being an arbitrary value), but even so the difference between the two groups was significant.
- Is there anything else I can do?
- And how would I report such a process in my thesis?