Sequential and Concurrent Mixed-Mode Designs: A Tailored Approach

Due to rising costs and declining response rates, surveys are increasingly moving from face-to-face interviewing to a self-administered mixed-mode design. Mixed-mode surveys can be conducted using a concurrent or a sequential design. A sequential design in which the web mode is offered first is a common strategy for mixed-mode surveys as it reduces survey costs. However, when deciding which mode choice sequence to use, sample balance should also be considered. One approach to achieving a balanced sample might be to tailor the sequence of the choice of modes, or the mode choice sequence. For this purpose, we use an indicator that assigns the sampled persons to the different mode choice sequences to minimize the variability of response probabilities. In this study, we compare the sample composition achieved with a concurrent and a sequential design. Additionally, we investigate whether indicator-based tailoring of the two mode choice sequences can improve sample composition. We implemented a randomized experiment in the 2021 German General Social Survey (ALLBUS), which surveyed the general population aged 18 and older in private households (N = 5,342) using a mixed-mode design (web and mail). In a first step, respondents were randomly assigned to a concurrent or a sequential design. We find that the two mode choice sequences lead to a similar sample composition. Next, we identify age as the best available single indicator of the variables known before the survey to tailor the mode choice sequence. Our analyses show that a tailored approach based on age improves the sample composition slightly.