Is there a "rule" to determine the minimum sample size required for a t-test to be valid?
For example, a comparison needs to be performed between the means of 2 populations.
There are 7 data points from one population and only 2 data points from the other.
Unfortunately, the experiment is very expensive and time consuming, and obtaining more data is not feasible.
Can a t-test be used? Why or why not? Please provide details (the population variances and distributions are not known).
If a t-test can not be used, can a non parametric test (Mann Whitney) be used? Why or why not?
Thanks a lot for your help! I know very little about stats, and have been searching around the internet for a detailed answer for some time.