A long history of returns.

Investing isn't easy. Even Warren Buffett counsels that most investors should invest in a low-cost index like the S&P 500. That way, "you'll be buying into a wonderful industry, which in effect is all of American industry," he says.

But there are, of course, companies whose long-term fortunes differ substantially from the index. In this series, we look at how members of the S&P 500 have performed compared with the index itself.

Step on up, IBM (NYSE: IBM).

IBM shares have, perhaps surprisingly, underperformed the S&P 500 over the last three decades:

Source: S&P Capital IQ.

Since 1980, shares returned an average of 11% a year, compared with 11.1% a year for the S&P (both include dividends). A thousand dollars invested in the S&P in 1980 would be worth $29,400 today -- and about the same amount if invested in IBM, naturally.

Dividends accounted for a lot of those gains. Compounded since 1980, dividends have made up 55.5% of IBM's total returns. For the S&P, dividends account for 41.5% of total returns.

And now have a look at how IBM's earnings compare with S&P 500 earnings:

Source: S&P Capital IQ.

Here we see some outperformance. Since 1995, IBM's earnings per share have grown by an average of 9.4% a year, compared with 6% a year for the broader index, with most of the difference taking place over the last few years alone. That's testament to the power of the company's ability to adapt over the years.

But that earnings-growth dynamic hasn't led to superior valuations. IBM has traded for an average of 21 times earnings since 1980, compared with 21.3 times for the S&P.

Add it all up, and IBM, to my surprise, has been a fairly average company for most of the last three decades.

The question is whether that will continue. That's where you come in. Our CAPS community currently ranks IBM with a four-star rating (out of five). Do you disagree? Leave your thoughts in the comment section below or add IBM to My Watchlist.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.