Using effect sizes to determine questionnaire sensitivity

Hi guys,

I ran a therapeutic group with 6 people and got them to complete 5 questionnaires before the group and repeat them after the group. I'm now writing this up as a report and I know I can't carry out t-tests as the sample size is so small, but I have been advised to report effect sizes to see if the questionnaires are sensitive enough to detect changes and therefore appropriate to use as a means of evaluating the therapeutic group.

I'm lost as to how to calculate these (would I work out the average total score for each questionnaire pre and post and compare these means using cohen's d?). Does a small effect size show that the questionnaires aren't sensitive enough?

I really appreciate any response anyone is able to give.

Many thanks