In order to justify the effort of selecting individual stocks, it's worth striving to beat the returns from a market index fund. But in any portfolio, there are likely to be some stocks that fall short of that benchmark. We regret to report that long term Cognex Corporation (NASDAQ:CGNX) shareholders have had that experience, with the share price dropping 45% in three years, versus a market return of about 19%. And more recent buyers are having a tough time too, with a drop of 23% in the last year.

While the stock has risen 3.6% in the past week but long term shareholders are still in the red, let's see what the fundamentals can tell us.

In his essay The Superinvestors of Graham-and-Doddsville Warren Buffett described how share prices do not always rationally reflect the value of a business. By comparing earnings per share (EPS) and share price changes over time, we can get a feel for how investor attitudes to a company have morphed over time.

During the three years that the share price fell, Cognex's earnings per share (EPS) dropped by 23% each year. In comparison the 18% compound annual share price decline isn't as bad as the EPS drop-off. So, despite the prior disappointment, shareholders must have some confidence the situation will improve, longer term. This positive sentiment is also reflected in the generous P/E ratio of 75.53.

The image below shows how EPS has tracked over time (if you click on the image you can see greater detail).

Dive deeper into Cognex's key metrics by checking this interactive graph of Cognex's earnings, revenue and cash flow.

A Different Perspective

Investors in Cognex had a tough year, with a total loss of 22% (including dividends), against a market gain of about 23%. However, keep in mind that even the best stocks will sometimes underperform the market over a twelve month period. Longer term investors wouldn't be so upset, since they would have made 0.5%, each year, over five years. If the fundamental data continues to indicate long term sustainable growth, the current sell-off could be an opportunity worth considering. While it is well worth considering the different impacts that market conditions can have on the share price, there are other factors that are even more important. Case in point: We've spotted 1 warning sign for Cognex you should be aware of.

If you are like me, then you will not want to miss this free list of undervalued small caps that insiders are buying.

Please note, the market returns quoted in this article reflect the market weighted average returns of stocks that currently trade on American exchanges.

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This article by Simply Wall St is general in nature. We provide commentary based on historical data and analyst forecasts only using an unbiased methodology and our articles are not intended to be financial advice. It does not constitute a recommendation to buy or sell any stock, and does not take account of your objectives, or your financial situation. We aim to bring you long-term focused analysis driven by fundamental data. Note that our analysis may not factor in the latest price-sensitive company announcements or qualitative material. Simply Wall St has no position in any stocks mentioned.