I have 3 groups, split by highest degree of education. For each individual in a group, i calculate the variance of her income in a five year window. Let's for simplicity assume that i only do this once, for one base year, and the group size does not vary over time in that window.
I then average the individual variances over all indivudals in a group, to compare the mean average income variance of the groups in that time window.
My second education group amounts to 2/3rds of the whole sample. I suspect the possibilty, that there is an overestimation (or even underestimation?) of the average variance in that group compared to the others, because more individual variances are added into it.
How would i go about confirming or denying my suspicion that i need comparable sample sizes for a comparison of average variances?
The smaller groups are about 400 - 600 individuals large, the big group holds about 2000 individuals.