This year turned out to be a busy one for the committee in charge of the S&P 500 (SNPINDEX:^GSPC). Seventeen companies were added to the storied index including well-known names such as General Motors (NYSE:GM), Delta Air Lines (NYSE:DAL), and Transocean (NYSE:RIG).

Using data from these companies and others, in the following video, Motley Fool contributor John Maxfield discusses the impact this has on stocks immediately after they're chosen for inclusion. Among other things, he finds that the average company added this year is up 9.1% since it became known that they were to be included on the index.

John Maxfield has no position in any stocks mentioned. The Motley Fool recommends General Motors and owns shares of Transocean. Try 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.