We then estimate the total cash holdings of firms (as a percentage of their book assets) as a function of the effective tax rate and standard determinants of cash.5 We control for firm size (the natural log of sales), for whether the firm has a bond rating, for its asset tangibility (the ratio of PP&E to book assets), profitability (return on assets), R&D to sales, advertising to sales, market to book ratio, book leverage, and capital expenditure to assets.6 This data is from Compustat. All variables are winsorized at the 1st and 99th percentiles.