The volatility of interest rates and the deregulation of the mortgage lending sector have meant that many homeowners also own mortgages at terms more favorable than current interest rates. This paper presents a model of residential mobility decisions and an empirical analysis that evaluates the importance of the ownership of these mortgages upon the mobility of homeowners. The results, based upon proportional and nonproportional hazard models, indicate that these effects are quite large. The empirical analysis distinguishes between different regulatory regimes that govern the assumption of existing mortgages, and indicates the implications of these findings for the pricing and valuation of mortgage-backed securities.

A computer simulation model in the tradition of evolutionary models of technical change is developed in this paper. It focuses on R&D competition in new product introductions and is based on data for the U. S. pharmaceutical industry during the 1970s. The sensitivity of innovation levels to the rate of generic competition, regulatory review time, and patent life is examined in the computer simulation experiments. These factors are found to have significant long-run effects on industry structure and innovation levels.

Imagine that one player, the “incumbent” competes with several “entrants”. Each entrant competes only with the incumbent, but observes play in all contests. Previous work shows that, as more and more entrants are added, the incumbent's reputation may dominate play of the game, if the entrants are faced in sequence. We identify conditions under which similar results obtain when the entrants are faced simultaneously, and we find specifications in which adding more simultaneous entrants has a dramatically different effect. We also show that, with either sequential or simultaneous play, incumbents need not prefer the situation in which their reputations can and do dominate play to the “informationally isolated” case in which each entrant observes only play in its own contest.

In this paper we report a generalization of the results of Foley and Guesnerie on the second welfare theorem to economies with arbitrary nonconvex production sets. The nature of marginal cost prices in such economies is clarified through the use of the Clarke tangent cones.

In models where both investors and securities are subject to differential taxation, there may be no set of prices that rule out infinite gains to trade, or "tax arbitrage."This paper characterizes the joint restrictions on financial-asset returns and investors' tax schedules that preclude tax arbitrage in the absence of short-sale constraints.The authors show that, if there exists any configuration of marginal tax rates on investors' tax schedules that rule out infinite gains to trade, then "no-tax-arbitrage" prices will exist.They also show that the existence of "no-tax-arbitrage" prices ensures the existence of equilibrium prices. THE EFFECTS OF DIFFERENTIAL taxation on the equilibrium prices of financial assets have attracted much attention from financial economists in recent years.Otherwise identical securities that contribute to taxable income to different degrees will, in general, be valued differently by taxable investors.As a result, tax considerations have been useful in helping explain the effect of dividend yield on stock returns,' the effect of coupon levels and term to maturity on bond prices,2 the timing of investors' portfolio transactions,3 and the observed capital structures of firms.4While a rich set of observed behaviors can be better understood by reference to differential taxation, there are well-known difflculties in dealing with taxes in a general-equilibrium setting.To clear markets, relative prices must reflect the marginal rates of substitution of all agents simultaneously.When tax rates differ across investors, however, this condition can be impossible to achieve.To illustrate, consider a world of perfect certainty with two assets: a tax-exempt municipal bond and a taxable government bond.To equate marginal rates of substitution, the rate of return on the government bond, rg, must equal that on the municipal, rm, "grossed up" by one minus the investor's marginal tax rate, ti; that is, rg = rm/( 1 -ti).If there are investors in more than one tax bracket, this condition will obviously be impossible to satisfy for all of them simultaneously.

Stiglitz and Weiss reply regarding credit rationing in markets with imperfect information.