This dissertation examines the relationship between debt and investment-related tax shields using changes in these classes of tax shields scaled by expected operating earnings following the passage of the Economic Recovery Tax Act(ERTA) in 1981. The substitution effect predicts that a negative relationship between changes in the two classes of tax shields will be observed in response to the increased investment-related tax shields offered by ERTA. Debt tax shields should decrease following ERTA since the probability of losing the tax benefit of tax shields would rise as investment-related tax shields increased following ERTA. Firms' probability of losing the deductibility of tax shields is used to segregate the sample into two groups. For the group of firms with a low probability of losing the deductibility of tax shields, the substitution effect is inapplicable and the relation between changes in the two classes of tax shields simply represents the debt securability effect. Since fixed assets can be used as collateral for debt, the debt securability hypothesis predicts a positive relationship between changes in debt and investment-related tax shields after the passage of ERTA. The model developed to segregate debt securability from the substitution effect reveals that, as predicted, the debt securability effect is positive for all firms and that the substitution effect is negative for those firms with a large probability of losing the benefits of tax shields. This reverses the findings of prior research. Controls for pecking order theory effects are introduced into the model to assure that the substitution effect observed is not due to debt ratio as predicted by Myers (1984). The findings described above remain intact except that the debt securability effect does not exist and the substitution effect is weaker for high-debt firms. Furthermore, support is offered for the pecking order theory. These results are robust to alternate specifications of time periods tested, variable definitions, data screening criteria and model specifications.

For investors in a given tax bracket, bonds with certain combinations of price and maturity may dominate other bonds. If markets are complete, S. M. Schaefer proved that a prohibition on short sales will give rise to tax-induced clienteles. Thus, bonds classified into groups by price and maturity may be held by investors in different tax brackets. Because of the tax advantages associated with discount bonds, there should be a tendency for high tax bracket investors to hold discount bonds and for low tax bracket investors to hold par and near-par bonds. An empirical consquence of this is that the after-tax term structure and implied tax rates may be different across different sets of bonds. The objective of this study is to test empirically for tax-induced clienteles in the market for government bonds with a regression methodology. Nonlinear least squares is used to simultaneously estimate the after-tax term structure and the corresponding implied tax rates. The estimation is performed on each group separately and on the entire sample. The null hypothesis is that the sets of parameters describing the after-tax term structure are equal across the groups. The alternative hypothesis, which will be termed the tax clientele hypothesis, is that sets of parameters are not equal across the groups.