This essay argues that management's resistance to majority voting bylaws (MV), could have caused an omitted-variable bias in testing MV effects on votes withheld.

By resisting MV bylaws - either by attempting to exclude shareholder proposals, relying on strict votes counting rules, or refusing to implement proposals that were voted favourably - managers could have both delayed an MV, and provoked frustrated shareholders into withholding their votes in annual elections, but only as long as resistance persisted. The very reason for the reported decline in withhold votes rates following MV implementation, thus, could have merely been an eventual shift in management resistance to MV.

While this response focuses on MV bylaws, it has general implications for testing the effect of shareholder' sponsored governance changes. 

Michal Barzuza, Unbundling the Dynamics of MV Implementation: Voluntary versus Reluctant Adoption of MV as a Source of an Omitted-Variable Bias, 83 University of Chicago Law Review Online, 242–254 (2017).