I posted a few times over the last month or so. I'm really hoping someone can at least leave a comment (to one or all three posts). We have data collected over the last year. Each month, we get some number of observations bucketed into a test group or a control group. Each month, we have been observing averages between the two groups (but no formal statistical test to compare the averages). Now, I have somewhere on the order of 60,000 observations in the control group and 4,500 observations in the test group. I want to compare the averages between groups, but the large difference in sample sizes scares me.