Does a digitalized single-mode survey lead to similar participation as a mixed-mode survey?

Abstract Background Choice of survey administration mode in surveys mapping public health may influence the participation rates and hence the generalizability of the results. The aim of the study was, in a randomized design, to examine whether three digital invitation letters (i.e., single-mode administration) lead to a similar participation as two digital letters and three physical letters (mixed-mode administration) mailed with a shorter time interval between reminders. Methods The study utilizes data on 10,000 individuals (≥20 years) who participated in The Danish Capital Region Health Survey in 2017 and were re-invited in 2021. Citizens who were registered to receive digital mail from public authorities were randomized into two groups; the intervention group that received three digital letters (day 0, 21, 46; N = 4,745), and the control group that received two digital letters (day 0 and 7) and three physical letters (day 23, 44, 68; N = 4,744). Participation rate in the intervention and control group was compared after the entire period. Furthermore, the two groups were compared in terms of increase in participation rate between first reminder and 14 days later, as well as after second reminder and 19 days later. Results The overall response rate was 69%, divided into 61% in the intervention group and 78% in the control group. After the first reminder, the response rate increased from 39% to 53% in the intervention group and from 34% to 53% in the control group, while the response rate after the second reminder increased from 54% to 60% in the intervention group and from 53% to 68% in the control group. Conclusions A digitalized single-mode survey with three digital letters led to a significantly lower participation rate compared with a mixed-mode survey with two digital and three physical letters. The results can create a better basis for choice of survey administration mode in future surveys. Key messages • Mixed-mode survey administration with multiple reminders leads to significantly higher response rates compared with single-mode surveys with fewer reminders. • Although it is more expensive and time-consuming, mixed-mode survey administration with multiple reminders should be considered in surveys to increase generalizability of data.