Abstract:
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While online panels offer a number of advantages, such as flexible data collection, they have often been criticized with regard to the accuracy with which they represent the intended target population. As a response to this criticism, probability-based online panels have developed strategies to cover the offline population as well. There are two dominant approaches on how to include the offline population in a probability-based online panel. One approach is to apply a mixed-mode panel design where the offline population is surveyed using an offline mode of data collection while the online population is interviewed online. The other approach is to provide offline households with the necessary equipment to participate online. In our study, we investigate the consequences that these two approaches have on the accuracy of the gathered survey data over time regarding sample composition and attrition. We use data from two large-scale probability-based online panels in Germany: the GESIS Panel, which applies a mixed-mode panel design where the offline population receives postal mail surveys, and the German Internet Panel (GIP) where offline households are provided with Internet equipment.
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