Social Transmission Bias: Evidence from an Online Investor Platform

Using data from a Twitter-like investor social platform, we document evidence consistent with self-enhancing transmission bias. We find investors are more likely to post about their better-performing stocks. Their followers are more likely to buy the posted stocks than other non-posted stocks. The effect of the postings on follow-up purchases is consistent with an attention-based interpretation: the postings bring the discussed stocks into the followers’ choice set and increase their purchases. We also find that postings’ effect on follow-up purchases is related to postings’ perceived credibility. The performance-postings relationship is stronger among more volatile stocks and the relationship between postings and follow-up purchases is stronger among stocks with higher recent returns, shedding light on the spread of high-variance and extrapolative strategies. We also document that the social network features influential nodes.