When you invest in the American stock market, you are looking to make a profit, build up savings for retirement, avoid loss, and grow your wealth. Whether you are investing in individual stocks or an ETF that tracks the market, two values are important. What can you buy a stock for today and what will it be worth at a future date. Since the current stock or ETF price is readily available, what you need are predictors of stock performance going into the medium to distant future.