This paper generalizes a model of monopolistic competition attributable to Spence (1976). Firms produce symmetrically differentiated products with declining or U-shaped average costs. Free entry drives profits to zero in equilibrium. Spence finds that when firms behave "competitively," in a...

Existing studies of household stock trading using administrative data offer conflicting results: discount brokerage accounts exhibit excessive trading, while retirement accounts show inactivity. This paper uses population-wide data from PSID and SCF to examine the overall extent of household...