I am performing stratified random sampling on a population (country) containing ~20 strata (states). I need to calculate mean of the population. I also know the proportion of the strata. My question is: Should I have a minimum sample size (say >=30) in each strata/state? I have greater than 30 samples for the country, but I do not have greater than 30 samples for each state. My assumption is since I am calculating mean for the population (country), at a state level, I can as well have 1 or 2 samples.
Will this be an issue in estimating the means? Please let me know.