1 Introduction
The mass media has been one of the most popular information sources, and there were few methods to directly measure their influences before social media appeared. Emergence of social media gave us ways to research interests of people from their contents. Our use of media has changed dynamically in the last decade, and has affected our societal behaviors. We now usually watch both mass media, and social media such as blogs, Twitter, and Facebook in our daily lives. Both types of media often influence each other. Many users write articles on social media about topics in TV programs, and TV shows occasionally take up topics that many people discuss on social media. We can therefore investigate influence of mass and social media by complementary analyzing trends in both media. It is important for marketing, politics, and sociology to analyze what kinds of topics have spread through mass or social media, and to analyze differences between multiple media.