How does the 'efficient market hypothesis' influence the potential benefits of active portfolio management, and what evidence challenges this hypothesis?

The efficient market hypothesis (EMH) posits that asset prices fully reflect all available information, making it impossible for investors to consistently outperform the market through active portfolio management. Under the EMH, any attempt to pick stocks or time the market is futile because prices already incorporate all known factors. This implies that passive investment strategies, such as index funds or ETFs, which simply track a market index, are the most rational approach, as they provide market returns at a low cost. The EMH challenges the notion that active managers can generate alpha (excess returns) by identifying undervalued securities or predicting market movements. However, considerable evidence challenges the EMH. Behavioral finance highlights cognitive biases that cause investors to make irrational decisions, creating market inefficiencies that active managers can potentially exploit. Anomalies like the small-firm effect (small-cap stocks outperforming large-cap stocks), the value premium (value stocks outperforming growth stocks), and momentum effects (stocks with recent high returns continuing to outperform in the short term) suggest that market prices do not always accurately reflect fundamental value. Furthermore, the success of some active managers over long periods provides empirical evidence against the strong form of the EMH, which asserts that even private information cannot be used to generate superior returns. Despite the EMH, many investors believe active management can add value, particularly in less efficient markets or by employing specialized strategies.