An invitee does not have to invite others – they must weigh the risks and benefits of inviting themselves. The invitee is not necessarily participating in the study. They may have just happened to come across the participant recruitment page, and thought it was interesting, and therefore shared it with others.
There may be unique circumstances when seeing the number of friends participating could be a problem for a study. Under normal circumstances, this feature increases the credibility of the study within a social network without identifying who in a potential participant’s social network is actually engaged.
The number of friends participating feature may be hidden on studies at the “Advanced Level.”
For more information on participant requests to interact with their data electronic form please see the Final Omibus Rule p.5634 (so a search in the doc for 5634 as it is not a page number).