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We study the conditions under which an internet platform excessively collects personal information when information externality exists. A monopolistic platform runs two-sided business where users and firms form each side. Users do not pay fees to the platform, but firms pay for targeted advertisements. In an environment where marginal information externality is large, the amount of personal information collected exceeds social optimum i) when the utility of marginal user does not make up for the aggregate disutility of existing users and firms and ii) when the platform extracts large markup from firms to keep users.

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This paper aims at analyzing both positive and negative political campaigns which affect voters’ perception about candidate valence. Consider the situation where candidates know valences each other but the voters cannot observe one candidate’s valence. We characterize perfect Bayesian equilibria, which depend on the cost of positive campaign for the candidate and the cost of negative campaign against the opponent. The cost may be interpreted as the campaign budget constraint or the risk from backfire. We show that there always exist a pooling equilibrium and, for a wide range of parameters, a separating equilibrium. If positive campaign costs sufficiently less by the candidate with higher valence, the high valence candidate conducts positive campaign whereas the low valence candidate does not. More important, if negative campaign against the high valence opponent is sufficiently costly or risky due to backfire, the incumbent conducts negative campaign against a low valence challenger but not against a high valence one. We also show that, the smaller the valence difference is between two candidates, the larger the platform divergence becomes on the equilibrium.

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This paper investigates sources of business cycles in Korea to shed some lights on the role of limited participation in financial market along the line of Christiano (1992) and King and Watson (1996). For this purpose, the paper sets up a small open economy model with two agents subject to limited participation in financial markets. Applying Watson (1993)'s measure of fit to evaluate the role of limited participation over Korean business cycles, it finds that the household's limited participation has played an important role in the business cycle in Korea after the Asian financial crisis.

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The aim of this paper is to discuss implications of important macroeconomic changes observed since 2000 on the further development of DSGE models. The starting point is to ask if the most recent DSGE model is flexible enough to allow for the possibility of the persistent drop in the growth rate of potential GDP observed in the Korean economy. The other topics include the relation between economic crisis and inequalities, the implications of observed jobless recoveries on the specification of labor market in DSGE models, macroeconomic impacts of household debt and government debt.