Does board independence constrain insider opportunism?

We examine whether insider opportunism is reduced by board independence. Using a sample of 18,194 firm-year observations over the period 1996–2016, we show that board independence constrains opportunistic insider trading. Our identification strategy uses the Sarbanes–Oxley Act of 2002 (SOX Act) and associated changes to the listing rules of NYSE/NASDAQ as a source of exogenous shocks in board independence. Our results are economically significant as insider opportunism declines by about 10.5%. We find that insider trading restrictions is the channel through which board independence reduces insider opportunism. Our additional analyses show that in competitive and R&D (research and development) intensive firms, the impact of board independence on opportunism is less pronounced. We also find that board independence constrains opportunism only in less complex firms. However, in co-opted boards, independent directors are less effective. Overall, we support the monitoring channel of board independence for reducing insider opportunism. JEL Classification: G14, G34, G40