If the stock market is at least semi-strong efficient then, (a) you should be able to determine when to buy or to sell a stock by studying the pattern of its historical prices.

(b) trading on information that you read in The Wall Street Journal or on the internet is unlikely to allow you to purchase stocks that are significantly underpriced.

(c) you cannot expect to find underpriced or overpriced stocks even if you have inside information.

(d) you are likely to find underpriced and overpriced securities by conducting a thorough analysis of a firm's financial statements.