We address the question of whether the trading of retail investors causes stock price anomalies. Our intent is to study settings in which retail investors are most likely to have influence on market prices. Previous research suggests that retail investors have more influence in small capitalization stocks, and argues that retail investors are most likely to be irrational. Most theories of stock price anomalies hypothesize the presence of irrational traders. Consequently, we focus on stock price anomalies in primarily small capitalization stocks. Our data are from the Australian Stock Exchange Clearinghouse. The Australian stock market is characterized by a high level of direct stock holdings by individual investors, further enhancing the likelihood of retail investors' influence. We investigate the Granger causality between investor category trading and stock prices, and display the relative trading volume of the investor categories. We conclude that retail investors are not responsible for stock mispricing. Since retail investors do not affect prices in this carefully selected environment, we infer that their trading is unlikely to influence stock market prices. Our conclusion has important implications for theories, particularly behavioral finance theories, that are dependent on the influence of retail investor trading in stock markets.