You have learned that a basic principle in portfolio management is the diversification of securities. Even if all stocks are priced fairly, each still poses firm-specific risk that can be eliminated through diversification. Therefore, rational security selection, even in an efficient market, calls for the selection of a well-diversified portfolio, providing the systematic risk level that the investor wants. Even in an efficient market investors must choose the risk-return profiles they deem appropriate.
The efficient market hypothesis (EMH) states that a market is efficient if security prices immediately and fully reflect all available relevant information. If the market fully reflects information, the knowledge of that information would not allow an investor to profit from the information because stock prices already incorporate the information. … Read the rest