Effects of a Time-Limited Push-to-Web Incentive in a Mixed-Mode Longitudinal Study of Young Adults

Abstract

This paper describes the impact of a time-limited push-to-web incentive on response rate and sample composition in a mixed-mode longitudinal study of young adults in the UK. An early bird push-to-web incentive experiment was conducted in the eighth follow-up of the Next Steps cohort study, which follows the lives of a nationally representative sample of around 16,000 people in England born in 1989-90. During the study ‘soft launch’ which tested procedures for the main stage of fieldwork, a randomly allocated group of study members was offered a time-limited £20 incentive to complete the survey online within three weeks of receiving the study invite; the incentive dropped to £10 after the three-week period and was no longer conditional on mode of completion. The control group was offered a standard £10 incentive conditional on completing the survey irrespective of mode and time. The time-limited £20 incentive was subsequently offered to all study members in the main stage of fieldwork. Here we investigate the impact of the early bird web-push incentive on response rates - after three weeks and by the end of fieldwork - and assess whether it had a differential impact on subgroups hence affecting the sample composition. Our analysis shows that the early bird incentive significantly increased web response rates during the time-limited period. By the end of fieldwork, however, it achieved similar response rates as the group offered the standard £10 incentive. The web response rates for the group offered the time-limited incentive remained higher throughout fieldwork. We found no evidence for an impact of the time-limited incentive on the sample composition in terms of key demographic and survey behaviour characteristics. The time-limited incentive performed in a similar way during the main stage of fieldwork in which all study members were initially offered the £20 incentive.