The Short Version
A broad, multi-market evidence base spanning 2015–2026 confirms that market-moving financial rumors on social media are associated with measurable increases in short-term stock volatility. Studies using GARCH models, rumor indices, and intraday analyses across Chinese, South African, U.S., and U.K. markets consistently find statistically significant effects. However, the relationship is stronger for negative rumors, more pronounced in retail-dominated markets, and complicated by reverse causality — high volatility can itself drive social media activity. These caveats are material but do not negate the core claim.