Does seating location impact voting behavior on Food and Drug Administration advisory committees?

Food and Drug Administration (FDA) advisory committees have a significant influence on patterns of clinical practice worldwide. Recent guidance to the committees by the FDA has focused on attempting to eliminate sources of bias due to committee voting procedures. Nevertheless, major sources of social influence have not been addressed. We analyzed transcripts of Circulatory Systems Devices Panel meetings from 1997 to 2005 in which the panel cast votes on premarket approval and for which a voting minority existed. Committee members who are assigned to speak later are significantly more likely to be in the voting minority (P < 0.001). This effect holds for meetings with sequential voting (P = 0.0058) and for meetings with simultaneous voting (P = 0.045). A weaker effect shows that, for meetings with sequential voting, committee members who vote later are significantly more likely to be in the voting minority (P = 0.018). Speaking order and voting order are both determined by seating location. We therefore conclude that voting behavior on FDA expert advisory committees is strongly associated with seating location. This suggests the presence of a possible social dynamic that is not addressed by existing FDA committee procedures.