I am working with two data sets of unequal sample sizes of 998 and 857. Average of first (998 samples), come out to be higher than the other dataset. To my surprise, when I split my complete data into unequal halves; first into 803 and 195 samples and other also into 819 and 38 samples. then comparison of average values of 803 subset of first complete dataset with the average of 819 subset of second complete data set showed a reverse trend in their mean values. Same reverse trend was observed with other subset of both the data set.
My question is that is it possible that if mean of total items in A>B, their two subsets showed reverse trend in their means i.e. mean of A1
Is this because of unequal sample sizes???? or because of sample density distribution trend????? or both????
If this is possible also, then is there any way to explain this quantitatively??????
It would be really helpful, if anyone can help me on this..