We investigate panel conditioning effects in a long-running probability-based online panel of the general population through a large-scale experiment conducted in 2020. Our experiment was specifically designed to study the effect of intensifying the surveying frequency for the treatment group (N = 5,598 panel members) during a 16-week corona study while keeping the control group (N = 799 panel members) at the usual bi-monthly surveying frequency. Our results show that panel conditioning is only a minor issue when increasing surveying frequency and only matters for survey questions directly related to the corona study. With this study, we contribute to the general panel conditioning literature, which is still unclear about the conditions under which conditioning effects may occur. In addition, while many panel surveys have conducted add-on studies with increased surveying frequency during the COVID-19 pandemic, ours is among the very few which can provide experimental evidence regarding the potential impact of the add-on study on the underlying panel data infrastructure.
