In this study, we examine the economic incentive to select political bias of news on Internet portals. The news slant is measured based on the expressions in congressional speeches in 2015, following Gentzkow and Shapiro (2010). The whole articles posted on two major domestic portals in the same year are used for the analysis. The higher the index value, the stronger the slant toward the ruling party. As a result, both portals locate somewhat farther from the ideology of the ruling party. Also, as the difference between portal and user increases, the number of clicks on news page decreased. The slant of portal was positively correlated with consumer 's political preference. In other words, consumers try to click on more news close to one’s preference, and the portal seems to select the news contents accordingly. We can interpret this as a profit maximization strategy of the portals in the online advertising market. In addition, there is a differentiation effect between the two portals regarding the news slant, but the size is small. These results suggest that a further discussion on the relevance and effectiveness of self-regulation in the portal news industry is necessary.

Preface
Executive Summary

Chapter 1 Introduction
　Section 1 Research Objectives
　Section 2 Literature Review
　Section 3 Domestic Internet News Market and Portal Behavior

Chapter 2 Data Construction and Bias Estimation
　Section 1 Data Collection
　Section 2 Estimation of Political Bias in Portals and News Outlets
　Section 3 Results of Portal News Bias Estimation

Chapter 3 Public Opinion Survey Results and Internet Users' Bias
　Section 1 Public Opinion Survey Results and Bias
　Section 2 Estimation of Portal Users’ Preference for the Ruling Party

Chapter 4 Bias and Consumer Behavior

Chapter 5 Selection of Bias by Portals
　Section 1 Influence of Portal Users
　Section 2 Competition and Differentiation Between Portals

Chapter 6 Conclusion and Policy Recommendations

References
Appendix
ABSTRACT