While online panels offer numerous advantages, they are often criticized for excluding the offline population. Therefore, some probability-based online panels have developed offline population inclusion strategies. Two dominant approaches prevail: providing internet equipment and offering an alternative survey participation mode. We investigate the impact of these approaches on two probability-based online panels in Germany: the German Internet Panel, which provides members of the offline population with internet equipment, and the GESIS Panel, which offers members of the offline population to participate via postal mail surveys. In addition, we explore the impact of offering an alternative mode only to non-internet users versus also offering the alternative mode to internet users who are unwilling to provide survey data online. Albeit lower recruitment and/or panel wave participation probabilities among offliners than onliners, we find that including the offline population has a positive long-term impact on sample accuracy in both panels. In the GESIS Panel, the positive impact is particularly strong when offering the alternative participation mode to non-internet users and internet users who are unwilling to provide survey data online.

虽然在线座谈会提供许多优势，但他们经常因排斥离线群体而受到批评。因此，一些基于概率的在线小组已经开发了离线人口包含策略。主要有两种主要方法：提供互联网设备和提供替代的调查参与模式。我们研究了这些方法对德国两个基于概率的在线小组的影响：德国Internet小组为离线人群提供互联网设备，而GESIS小组为离线人群提供了邮政服务。调查。此外，我们探讨了仅向非互联网用户提供替代模式的影响，以及向不愿在线提供调查数据的互联网用户提供替代模式的影响。尽管离线用户的招募和/或小组参与的概率要低于在线用户，但我们发现，包括离线人群在内的两个小组的样本准确性都具有长期的正向影响。在GESIS小组中，当为不愿在线提供调查数据的非互联网用户和互联网用户提供替代参与模式时，其积极影响尤其明显。