No surprise but in can case you were wondering, retail investors trade mostly on noise. A little bit more surprising is that the effect is to make markets less liquid since some models suggest that noise traders make markets more liquid and accurate by bringing in the sharks.
Contrasting with recent evidence that retail traders are informed, we find that Robinhood ownership changes are unrelated with future returns, suggesting that zero-commission investors behave as noise traders. We exploit Robinhood platform outages to identify the causal effects of commission-free traders on financial markets. Exogenous negative shocks to Robinhood participation are associated with increased market liquidity and lower return volatility among stocks favored by Robinhood investors, as proxied by WallStreetBets mentions. Platform outages are also associated with reduced high frequency trader (HFT) activity, indicative of payments for order flow. However, outages have the strongest effect on stocks neglected by HFTs, suggesting that zero–commission traders have direct negative effects on market quality.