In the following video, Fool contributor Matt Thalman discusses one reason investors should avoid buying mutual funds and stick to an index fund. Today he focuses on returns.

When the average investor is considering what to buy for retirement, based on historical numbers the best option is a simple S&P 500 index fund or perhaps a Russell 2000 fund. While some mutual funds may beat the S&P 500 over short time frames, Matt says, very few consistently outpace the S&P 500 over longer periods of time.

Check back Monday through Friday as Fool contributor Matt Thalman explains what caused the Dow's winners and losers of the day, and every Saturday for a weekly recap. Follow Matt on Twitter: @mthalman5513Try any of our Foolish newsletter services free for 30 days. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.