Response Rates in the European Social Survey: Increasing, Decreasing, or a Matter of Fieldwork Efforts?

Response rates are declining increasing the risk of nonresponse error. The reasons for this decline are multiple: the rise of online surveys, mobile phones, and information requests, societal changes, greater awareness of privacy issues, etc. To combat this decline, fieldwork efforts have become increasingly intensive: widespread use of respondent incentives, advance letters, and an increased number of contact attempts. In addition, complex fieldwork strategies such as adaptive call scheduling or responsive designs have been implemented. The additional efforts to counterbalance nonresponse complicate the measurement of the increased difficulty of contacting potential respondents and convincing them to cooperate. To observe developments in response rates we use the first seven rounds of the European Social Survey, a biennial face-to-face survey. Despite some changes to the fieldwork efforts in some countries (choice of survey agency, available sample frame, incentives, number of contact attempts), many characteristics have been stable: effective sample size, (contact and) survey mode, and questionnaire design. To control for the different country composition in different rounds, we use a multilevel model with countries as level 2 units and response rates in each country-year combination as level 1 units. The results show a declining trend, although only round 7 has a significant negative effect.