The analysis of motivations for the endorsement activity identified only three scales (see Table 6). As with the question-answering activity, the Expertise scale was rated significantly higher than the Enjoyment and Build Community Ties scales. Like the question-answering activity, no statistically significant difference was found between the Enjoyment and Build Community Ties scales. The Kruskal–Wallis test of the scales on seniority groups found significant differences only for Expertise. Postdocs had the highest mean rank for the scale, significantly higher than that for assistant professors (see Fig 5). This last finding is quite intriguing and warrants further investigation. One can only suggest that postdoctoral appointments are typically research-only appointments. On the other hand, in addition to conducting research, assistant professors might be responsible for and have a need to promote their own graduate students and postdoctoral researchers, as well as to build and maintain ties with other colleagues at their institutions or in a greater research community to receive promotion and tenure. Hence, assistant professors may prioritize other motivations, such as group loyalty, when making endorsements. Rashid and colleagues  showed that members of an online information system were more willing to make contributions when those contributions benefited smaller groups they were part of rather than the general community. One full professor noted that he made endorsements “to support [his] junior faculty, colleagues, and graduate students” (S9).