The response rate is the proportion of returned questionnaires compared to the number of questionnaires sent out. Low response rates are a problem insofar as they jeopardize the representativeness of an investigation. The reason is that certain groups of people participate disproportionately in the answer and thus the results can be distorted (e.g. certain age groups, occupational groups or from certain regions). One possible solution is the quota return control.
There are various ways of increasing the mostly low response rate from written surveys. Example: In a cover letter, the importance of the answer or the benefit for the respondent is pointed out. Raffle campaigns or gifts for each participant can also increase the response rate.