EconAir

    WHY STOCK PRICES GO UP   The movement of a stock index such as the S&P 500 or an individual stock depends on two things:   Earnings per share (EPS) and changes in EPS. Stock price/earnings per share ratio (PE ratio) and changes in the PE ratio.   If the PE ratio stays the same, an increase in EPS leads to an increase in the stock price. The same is true of a stock index. Rising EPS combined with a rising PE ratio is often the reason why a stock goes up more than the average stock.   Well, that was easy. Well, not really.   The stock market is “forward-looking,” that is, it tries to anticipate changes, especially changes in EPS and the PE ratio. There is a great amount of forecasting. But since the forecasted changes are in the future, they are inherently uncertain. The forecasts of some companies’ EPS are more uncertain than others. Some are very uncertain. For example, the future sales and earnings of a small biotech company may depend on the success of a clinical trial and FD

This primer is aimed at the long-term investor. But this does not mean that you should necessarily hold all of the stocks and funds in your portfolio for a long time. WHY STOCK PRICES GO UP The movement of a stock index such as the S&P 500 or an individual stock depends on two things: Earning per share (EPS) and changes in EPS. Stock price/earnings per share ratio (PE ratio) and changes in the PE ratio. If the PE ratio stays the same, an increase in EPS often leads to an increase in the stock price. The same is true of a stock index. Rising EPS combined with a rising PE ratio is often the reason why a stock goes up more than the average stock. Since 2009, the beginning of the stock market recovery from the last recession, most of the increase in stock prices has been due to the increase in earnings per share (EPS). Well, that was easy. Well, not really. The stock market is “forward-looking,” that is, it tries to anticipate change, especially cha