For my research in psychology, I created an assessment tool to measure symptom X in a clinical (n = 10) and a non-clinical (n = 10) sample. I want to verify whether the overall average score obtained by the clinical group on the measure differs from that of the non-clinical group.

The measure involves a 1 to 5 scoring scale which is applied four times to the same person on four tasks; as such, four scores are obtained per person from which I derive one final average score per person on the measure (i.e., scores of 3, 3, 2, 1 = 9; 9/4= 2.25, so 2.25 is the person's average score on the measure).

In SPSS, my first variable is each participant's final average score on the measure. My second variable is their group (clinical = 1 or non-clinical = 2). I think I would be using a non-parametric t-test for 2 independent samples due to how small my sample is; however, I am unsure. Can I use a parametric t test for 2 independent samples? I know I need to verify whether my distribution is normally distributed or not. I have done this doing a visual scan of a histogram for each group, and my distribution appears normal for the non-clinical sample (as per a visual scan of data); however, it is skewed for the clinical-sample. I am unsure how to proceed to answer my initial question, or whether there might even be a more optimal way to organize my data in SPSS.

Any help is greatly appreciated!

OS = Windows 8, and I have used version 17.0 of SPSS.