U.S. stock futures were little changed on Thursday night after the major averages slid following a lackluster earnings forecast from retail giant Walmart. Dow Jones Industrial Average futures were trading near the flatline, as were S&P 500 futures and Nasdaq-100 futures.

However, the S&P 500 ( ^GSPC 0.24%) 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.

Wall Street is retreating from its record as a slide for Walmart weighs on U.S. stock indexes Thursday. The S&P 500 was down 0.6% in morning trading after setting all-time highs in each of the last two days.