“…20 In all specifications, we control for a number of other variables that might be correlated with both changes in tax rates and changes in executive pay: the executive's job title in the previous year and whether this title changed in the current year, whether the executive sat on the board of directors in the previous year and whether their director status changed in the current year, the firm's sales in the previous year (to proxy for firm size), the firm's market value in the previous year (another measure of firm size), the rate of return on the firm's stock price in the previous year (to capture past firm growth), the firm's leverage in the previous year (defined as the ratio of liabilities to assets), and the firm's market-to-book ratio in the previous year (to proxy for growth opportunities). An extensive literature in accounting and corporate finance shows that these variables have an effect on the level and structure of executive pay (see, for example, Smith and Watts 1992, Bizjak, Brickley and Coles 1993, Core, Holthausen, and Larcker 1999, Murphy 1999, Core, Guay, and Larcker 2008, Graham, Li and Qiu 2009). …”