Hello! I am working with survey data and want to merge two datasets. One dataset has biographical information and the other employment information (master) on individuals. According to the survey website, both datasets have the identifiers pid (personal id) and syear (survey year). I am, however, unsure whether to do a 1:1, m:1, or 1:m merge. I have tried all three ways, and no matter how I do it there are 566,044 unmatched observations, overwhelmingly from my master dataset, which seems extremely large. I have run a duplicates report of those sharing pid and syear for both datasets and there are no duplicates that share the two identifiers in either.

Code:
 merge m:1 pid syear using "C:\Users\zxoqi13\Downloads\biol.dta"
What could this mean? Is it ok that there are so many unmatched observations? What would you advise I look at (commands I could run) to determine what type of merge is appropriate?

Thank you!