Should Directors Have Term Limits? – Evidence from Corporate Innovation
基于1996-2006年美国企业数据，研究发现长期任职的外部董事显著减少企业专利数量与质量，降低研发效率和探索强度，且这种负面影响是因果性的，但可通过与CEO共事时间或兼任其他公司高管来缓解。
This paper examines the effect that directors with extended tenure have on corporate innovation based on a sample of US firms from 1996 to 2006. Using the propensity-score matched-pair research design, I find that firms with a higher portion of outside directors enjoying extended tenure produce significantly fewer patents and that these patents receive fewer subsequent citations. These firms also have lower research and development (R&D) productivity and exploration intensity than their matched control firms, although I found no significant difference in their R&D investment intensity. Difference-in-differences tests based on director deaths and regulatory changes in the early 2000s suggest that the adverse effect of long director tenure on innovation performance is causal. I also find that the effect is mitigated when long-tenured directors have more years of overlap in service with CEOs, and when long-tenured directors are executives at other firms. Finally, I find that boards with extended tenure attenuate the contributions of innovation outputs to future firm value and performance. These findings shed new light on the debate over length of board tenure and provide another justification for imposing term limits on directors.