Comparing heteroscedastic groups with sample sizes from 1 to 24… No valid tests?

I feel that this problem is a lot more complex and requires some more information for sound advice.

What exactly are you trying to compare with each group? Since your running an ANOVA how many ivs are you using, and how many levels does each IV have?

Are you trying to quantify that each group is different or are you trying to classify each group based upon each groups observations?

In the end I'd recommend that you bootstrap each group with more than one observation, and then see if you can merge the single observation group into another groups whose bootstrapped mean is close to the single observation. However that advice is completely contingent on what you are trying to accomplish.

/r/statistics Thread