Follow-Ups in Mail Surveys. Empirical Findings on the Effects on the Response Rate, the Responses and the Sample Composition

Abstract

The fact that reminders increase the response rates of mail surveys is empirically documented. However, only a few studies have dealt with the effect of follow-up mailings on both response behaviour and sample composition. This article investigates these aspects using data from a regionally representative mail survey (N=3.555) on crime at advanced ages among 49 to 81 years-olds that was conducted in Südbaden/Baden-Württemberg in 2009. The analyses showed that the use of follow-ups increased the number of missing values (item-nonresponse), with a curvilinear relation between the number of follow-ups and the extent of item-nonresponse. Follow-ups primarily involve people that are usually underrepresented in the first wave, i. e., people who are younger, living in rural areas, having a lower social status and weaker political interest. Using reminders therefore contributes to an enhanced social composition of the net sample. Nevertheless, the respondents of the first mailing do not differ fundamentally from those of the complete survey sample in terms of their social variables as well as their psycho-social characteristics. However, one exception is the respondents` criminal behaviour over the life-course: with increasing numbers of mailings the respondents` delinquency strongly decreases. Obviously, responses on the survey topic are thus correlated with the timing of data collection. This again shows how reminders can help diminishing biases. From a methodological point of view it is therefore recommended to always include follow-up mailings in postal surveys. Three mailings seem to be ideal.