The Causal Relationship between Social Media Sentiment and Stock Return : Experimental Evidence from an Online Message Forum

This paper examines the impact of sentiment in an online message forum on stock returns. Using a novel controlled experiment, we collect a large panel of messages with no fundamental information but strong sentiment and stock return data. We find a significant causal effect of social media sentiment on the same-day stock returns. The sentiment has no significant effects on stock returns on subsequent days. This effect is mainly driven by messages with positive sentiment, which has a strong positive impact on stock returns. Our results establish a causal relationship between social media sentiment and stock returns and highlight the risk of market manipulation via social media