The Trump Effect : A Case-Study of Immediate Stock Market Reactions to the President’s Company-specific Twitter Mentions 

Abstract: This thesis investigates how the U.S President’s Twitter mentions of individual companies’ investment announcements influence the short-term price of their stock. By assuming that the President’s comments on a company’s plans should be incorporated by markets as new information, testing the Efficient Market Hypothesis assumption that the markets incorporate all new information, the thesis seeks to contribute to a new, unexplored and growing, research field. This thesis utilizes a qualitative analysis method, studying Twitter mentions on the topic of Trump’s Tax Reform. The data in this thesis is derived from the President’s personal Twitter-account, company announcements, stock price charts, and the Standard & Poor’s S&P500 Index. To conclude, this study finds that although the President’s Twitter comments may signal his public approval of a company and its plans, it appears that any market reaction is only short-term, and that as the market incorporates additional information it returns to an informed state in terms of stock valuations. This study suggests that there are few observable indicators that Trump’s positive mentions on Twitter causes any significant market reaction.