Hi, I am using several datasets (>2) with a common variable 'identification' which is unique. After I merging the dataset second round, it appears 3 merge variables, with many unmatched observations (i.e. merge data1 and data2, save as data_a. then merge data_a and data3, then many unmatched observations appear). What should I deal with this? Also, after solving unmatched problem if possible, how should I deal with the merge variables? Can I just drop them?