Hi everyone. I am trying to merge two datasets constructed from German SOEP data. The datasets have been merged with each other and manipulated several times. No matter which option we try to use (m:1, 1:m, 1:1) or which variables to match with (person ID number, year), we get the same error saying that the variables do not uniquely identify the observations. We've done similar merges that have worked, no problem. The only thing we did before this that might have messed things up is changing the person ID number from one individual to the other in order to find the nationality of that individual using another dataset. In addition, the datasets were are using are very similar, they contain many of the same variables, this might also be a source of problems. If someone could give any suggestions for how to proceed it would be super helpful. Thank you!

Maria