*4.1. Limitations*

First, this study was a cross-sectional study, not a repeated-measurements design, so no causality can be directly inferred from the data regarding obesity surgery. However, as many other relevant variables have been measured and controlled across both groups, moderation effects of the surgery in the present sample can still be interpreted. Then, the presented data were collected by an online questionnaire, which necessarily holds some limitations. For instance, participant response rates cannot be controlled so that a participant bias seems plausible. In consequence, this lack of participant control may influence the results' generalizability. Furthermore, the possibility of selection bias should be considered.

Last, psychological COVID-19-specific traits reported here were not measured by validated instruments, simply because none existed to that date. Ahorsu et al. [53] created the first questionnaire to assess COVID-19-related fear after the present survey had been launched—the Preventive COVID-19 Behavior Scale (PCV-19BS, see [53,54]). Thus, COVID- 19-related fear and DSCED were self-generated items or at least adapted to assess COVID-19-specific traits. As can be seen in previous studies [17,18,33,54], however, this COVID-19-related fear item qualifies relatively well to assess fear, but not generalized anxiety, at the time of the pandemic. Despite being the first study on the influence of obesity surgery on COVID-19 distress, the study is limited in terms of gender differences. Of course, additional factors such as the connection to an obesity center should be considered.
