Invitation letters increase response rates in elite surveys: evidence from Germany and the United Kingdom

A key challenge when surveying political elites is recruitment. Low response rates can lead to biased samples and underpowered designs, threatening the validity of descriptive and experimental scholarship. In a randomized control trial, we test the effects of sending postal invitations in a large survey of local elected officials. We find that German and UK local politicians are more likely to complete the survey if invited by postal mail, rather than simply by email. Recruitment mode does not impact the quality of responses but shapes the population of local officials recruited. Officials invited via postal letter were more likely to come from smaller municipalities and less likely to have a college degree. Costs per response are relatively high but can be reduced as we learn more about selection into elite surveys.