Sample Representation and Substantive Outcomes Using Web With and Without Incentives Compared to Telephone in an Election Survey

摘要

The objective of this article is to understand how the change of mode from telephone to webaffects data quality in terms of sample representation and substantive variable bias. To thisend, an experiment, consisting of a web survey with and without a prepaid incentive, wasconducted alongside the telephone Swiss election survey. All three designs used identicalquestionnaires and probability samples drawn from a national register of individuals.First, our findings show that differences in completion rates mostly reflect different levelsof coverage in the two modes. Second, incentives in the web survey strongly increasecompletion rates of all person groups, with the exception of people without Internet access orlimited computer literacy. Third, we find voting behavior to be much closer to official figuresin the web with the incentive version compared to the two other designs. However, this ispartly due to the different sociodemographic compositions of the samples. Other substantiveresults suggest that the incentive version includes harder-to-reach respondents. Unit costs aremuch lower in the two web designs compared to the telephone, including when a relativelyhigh incentive is used. We conclude that in countries with high Internet penetration rates suchas Switzerland, web surveys are already likely to be highly competitive.