I have data from two different groups and they both have 19 subjects. I find a statistical measure for the two groups and claim that one is greater than the other. But this difference could have occurred due to some outliers in either of the group. To check for the robustness of the result I do the following. I randomly pick 10 subjects from each group and find the statistical measure. I do this for 100 different subsets of 10 subjects. Then I find the mean and SD of the 100 runs to do a two sample t-test and then to find the corresponding p-value. My question is what degrees of freedom (n) do I use to find the t and p value. Even though I have 100 observations from the 100 runs, I don't think I can use 100 since they are not independent observations. Many of the subjects are repeated in the subsets. Can anyone please help me to find the right n ?