On the basis of scientific literature, indicators for the three quality criteria were derived and subsequently operationalized with 36 single variables. The instrument was exemplarily applied to the portals TripAdvisor, Holidaycheck, Booking, HRS, Expedia, hotel.de, hotels.com, Venere, Zoover and Ebookers, whereby the data was collected by means of a content analysis of the respective websites. The results at the criterion level were aggregated to a comprehensive quality index for each portal. Each criterion was equally weighted. Seven theoretically plausible weighting variants at criterion and variable level were then tested in order to verify the robustness of the results. In doing so, the overall picture remained the same.
