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I have a population of interest on which one numeric variable has been measured twice: before and after surgery. I did a paired t-test to compare means of the variable. However, there is a difference in sample size between the pre-op and post-op groups, ie not all patients had the variable measured after the surgery so that the post-op group is smaller. The pairs of the variable are known and linked by patient ID so that I was able to perform a paired t-test on the known differences. How should I report the mean of the variable in both samples? Should I report the mean of the paired-t test (ie the mean of the variable from the patients that were actually compared), or the mean of the actual sample size? I don't if I'm being clear, but hopefully someone can provide me with some insight.