Abstract
BackgroundIncreasing availability of the Internet allows using only online data collection for more epidemiological studies. We compare response patterns in a population-based health survey using two survey designs: mixed-mode (choice between paper-and-pencil and online questionnaires) and online-only design (without choice).MethodsWe used data from a longitudinal panel, the Hygiene and Behaviour Infectious Diseases Study (HaBIDS), conducted in 2014/2015 in four regions in Lower Saxony, Germany. Individuals were recruited using address-based probability sampling. In two regions, individuals could choose between paper-and-pencil and online questionnaires. In the other two regions, individuals were offered online-only participation. We compared sociodemographic characteristics of respondents who filled in all panel questionnaires between the mixed-mode group (n = 1110) and the online-only group (n = 482). Using 134 items, we performed multinomial logistic regression to compare responses between survey designs in terms of type (missing, “do not know” or valid response) and ordinal regression to compare responses in terms of content. We applied the false discovery rates (FDR) to control for multiple testing and investigated effects of adjusting for sociodemographic characteristic. For validation of the differential response patterns between mixed-mode and online-only, we compared the response patterns between paper and online mode among the respondents in the mixed-mode group in one region (n = 786).ResultsRespondents in the online-only group were older than those in the mixed-mode group, but both groups did not differ regarding sex or education. Type of response did not differ between the online-only and the mixed-mode group. Survey design was associated with different content of response in 18 of the 134 investigated items; which decreased to 11 after adjusting for sociodemographic variables. In the validation within the mixed-mode, only two of those were among the 11 significantly different items. The probability of observing by chance the same two or more significant differences in this setting was 22%.ConclusionsWe found similar response patterns in both survey designs with only few items being answered differently, likely attributable to chance. Our study supports the equivalence of the compared survey designs and suggests that, in the studied setting, using online-only design does not cause strong distortion of the results.
Highlights
Increasing availability of the Internet allows using only online data collection for more epidemiological studies
Can differences in response patterns be explained by selection of participants with respect to sociodemographic characteristics? To validate differences found in response patterns, we investigated if these differences were specific to the online mode of participation
The response rate was highest in the oldest age group, i.e. between 65 and 69 years, but the effect was much stronger in the mixed-mode group (Fig. 2a)
Summary
Increasing availability of the Internet allows using only online data collection for more epidemiological studies. Several studies investigated how responses differed between online and non-online responders within mixed-mode surveys [9,10,11,12]. They showed that preferred survey mode was linked to sociodemographic factors; once adjusted for those baseline differences, the majority of differential responses disappeared [11, 12]. These comparisons do not encompass the situation where only one mode of data collection is offered, and those willing to participate are forced to use it. A further limitation of previous studies is the lack of adjustment for multiple testing, potentially overestimating the true differences between data collection modes
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