We are doing an evaluation in different organizations and need to get data from workers about their work behavior. As this information is something that could get workers in trouble, privacy is an issue, so we go for anonymized questionnaires. To connect the data over time, we are looking for a participant identifier. Based on prior experiences, asking for:
Kindly write down your participant code. This code consists of the first letter of your place of birth, the first letter of your own first name, the first letter of the first name of your mother, and your own day of birth.
has the disadvantage that some participants think that their colleagues or superiors can guess the code and there are always a few participants who do not know one parent. Also, participants make mistakes with this code.
So my question is -- is there a way to ask for a code that allows us to connect data over time (i.e., it is unique for a person), yet is also accepted by participants?
Update: I had a look at the answers here (thank you very much) -- one caveat, we are organizing the evaluation, but there are different researchers (separate institutions) visiting the sites. Meaning that keeping a list of the participants real names and their codes does not work (if one institution kept it, it would create a bottleneck). Ideally the code is something that is solely on the participants side.