Between 1993 and 2000, at least 18 countries saw publication of guidelines proposing minimum representation of outside directors on corporate boards. Underlying this movement is an apparent presumption that boards with significant outside directors will make different and, perhaps, better decisions than boards dominated by insiders. As the first-mover in this movement, the United Kingdom provides a laboratory for a “natural experiment” to examine this presumption empirically. We find that UK boards that complied with the exogenously imposed standard were more likely to appoint outside chief executive officers (CEOs). Additionally, announcement period stock returns indicate that investors appear to view appointments of outside CEOs as good news. Apparently, boards with more outside directors make different (and perhaps better) decisions.

We use hand-collected board data around the issuance of two distinct government-led board structure mandates in the U.K. to establish the effect of outside directors on acquirer performance. Increases in outside director representation are associated with better acquirer returns in deals involving listed targets, but not when the target is private. These results are consistent with greater outside director reputational exposure when publicity is high. While we do not advocate mandated board structures, our evidence suggests that the particular diktats we examine were associated with improved acquirer performance in public firm takeovers. We present corroborating evidence from the U.S. around a similar reform period.