I am collecting data from a population of about 150 or so, and also from a subpopulation within that of 10-15 which are receiving a specific treatment. I am aiming to compare their scores on the same measure, to see if this population receiving treatment is truly 'special' in some way, and that there is not a larger population that also requires this treatment. I am just trying to figure out what statistics to use, as t-test for some reason is not quite sitting right with myself or my supervisor.

Thanks for any help.