This paper examines the leadership of extreme action teams-teams whose highly skilled members cooperate to perform urgent, unpredictable, interdependent, and highly consequential tasks while simultaneously coping with frequent changes in team composition and training their teams' novice members. Our qualitative investigation of the leadership of extreme action medical teams in an emergency trauma center revealed a hierarchical, deindividualized system of shared leadership. At the heart of this system is dynamic delegation: senior leaders' rapid and repeated delegation of the active leadership role to and withdrawal of the active leadership role from more junior leaders of the team. Our findings suggest that dynamic delegation enhances extreme action teams' ability to perform reliably while also building their novice team members' skills. We highlight the contingencies that guide senior leaders' delegation and withdrawal of the active leadership role, as well as the values and structures that motivate and enable the shared, ongoing practice of dynamic delegation. Further, we suggest that extreme action teams and other "improvisational" organizational units may achieve swift coordination and reliable performance by melding hierarchical and bureaucratic role-based structures with flexibility-enhancing processes. The insights emerging from our findings at once extend and challenge prior leadership theory and research, paving the way for further theory development and research on team leadership in dynamic settings.

Evidence shows clearly that academic records, MMIs, aptitude tests, SJTs and SCs are more effective selection methods and are generally fairer than traditional interviews, references and personal statements. However, achievement in different selection methods may differentially predict performance at the various stages of medical education and clinical practice. Research into selection has been over-reliant on cross-sectional study designs and has tended to focus on reliability estimates rather than validity as an indicator of quality. A comprehensive framework of outcome criteria should be developed to allow researchers to interpret empirical evidence and compare selection methods fairly. This review highlights gaps in evidence for the combination of selection tools that is most effective and the weighting to be given to each tool.

Over two decades of research has indicated that group affect is an important factor that shapes group processes and outcomes. We review and synthesize research on group affect, encompassing trait affect, moods, and emotions at a collective level in purposive teams. We begin by defining group affect and examining four major types of collective affective constructs: (a) convergence in group affect; (b) affective diversity, that is, divergence in group affect; (c) emotional culture; and (d) group affect as a dynamic process that changes over time. We describe the nomological network of group affect, examining both its group-level antecedents and group-level consequences. Antecedents include group leadership, group member attributes, and interactions between and relationships among group members. Consequences of group affect include attitudes about the group and group-level cooperation and conflict, creativity, decision making, and performance. We close by discussing current research knowns, research needs, and what lies on the conceptual and methodological frontiers of this domain.

Grounded in a social functional perspective, this article examines the conditions under which group affect influences group functioning. Using meta-analysis, the authors leverage heterogeneity across 39 independent studies of 2,799 groups to understand how contextual factors-group affect source (exogenous or endogenous to the group) and group life span (one-shot or ongoing)-moderate the influence of shared feelings on social integration and task performance. As predicted, results indicate that group positive affect has consistent positive effects on social integration and task performance regardless of contextual idiosyncrasies. The effects of group negative affect, on the other hand, are context-dependent. Shared negative feelings promote social integration and task performance when stemming from an exogenous source or experienced in a 1-shot group, but undermine social integration and task performance when stemming from an endogenous source or experienced in an ongoing group. The authors discuss implications of their findings and highlight directions for future theory and research on group affect.

We develop a theoretical model, grounded in exchange theory, about the process through which relationships between entrepreneurs and investors develop and influence the growth of new ventures. Our theory highlights the multifaceted relationships that entrepreneurs and investors share-comprising both affective and instrumental dimensions-and the bidirectional exchanges of social and financial resources that build these relationships over time. An exchange theory perspective sheds light on the emergence of different patterns of relationship development over time and how different kinds of resource exchange contribute to new venture growth, contingent on the core problems that a venture faces at a given stage of development. We discuss implications of an exchange perspective on resources and relationships in entrepreneurship for theory, research, and practice. Both authors contributed equally to this article; our names are listed alphabetically. We are grateful to associate editor Joep Cornelissen and three anonymous reviewers for their helpful feedback throughout the review process. We also thank Ray Sparrowe and the members of the Wharton School's M-Squared group for their guidance on previous versions of the manuscript.