However, the S&P 500 ( ^GSPC -0.01%) is generally considered the best barometer for the overall U.S. stock market due to its scope and diversity. Read on to see the S&P 500's average return over the last decade, and to learn what Wall Street expects in the future.

U.S. stock indexes are edging lower in a relatively quiet Wednesday on Wall Street. The S&P 500 was down 0.2%, a day after setting an all-time high. The Dow Jones Industrial Average was down 163 points,