Criteria for Inclusion
The article abstracts were reviewed for content and considered for inclusion in the meta-analysis. If it was unclear from the abstract how leadership was measured or conceptualized, we performed a full-text search to determine if the study met our criteria. In accordance with our relationships of interest, several rules for study inclusion were established. First, the article needed to include measures of both shared leadership and performance at the team level of analysis. Second, teams used in each sample had to have multiple leaders during the study time frame. Notably, studies reporting indices of a leadership climate were excluded because climate does not necessarily imply shared leadership. We also excluded laissez-faire leadership effect sizes. Laissez-faire leadership is a component of Bass’s (1985) conceptualization of transactional leadership and refers to a “hands-off” leadership style where the individual does not engage in influence of team members. In other words, it refers to the absence of leadership. Third, teams must have engaged in some form of shared leadership. As articulated above, this includes instances where leadership is shared over time, team members provide leadership influence and may be engaged in different leadership roles or functions, and the distribution or engagement of leadership does not need to be equal across team members. In particular, investigations involving rotated leadership were included, but instances where only vertical power differentiation existed were not included. Finally, articles needed to report correlations between our primary variables of interest or provide statistical information needed to compute effect sizes.