If you are building a properly diversified stock portfolio, the chances are some of your picks will perform badly. Long term Canadian Solar Inc. (NASDAQ:CSIQ) shareholders know that all too well, since the share price is down considerably over three years. Regrettably, they have had to cope with a 66% drop in the share price over that period. The more recent news is of little comfort, with the share price down 43% in a year. On top of that, the share price is down 14% in the last week.

Since Canadian Solar has shed US$106m from its value in the past 7 days, let's see if the longer term decline has been driven by the business' economics.

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While the efficient markets hypothesis continues to be taught by some, it has been proven that markets are over-reactive dynamic systems, and investors are not always rational. One imperfect but simple way to consider how the market perception of a company has shifted is to compare the change in the earnings per share (EPS) with the share price movement.

During the three years that the share price fell, Canadian Solar's earnings per share (EPS) dropped by 29% each year. The 30% average annual share price decline is remarkably close to the EPS decline. That suggests that the market sentiment around the company hasn't changed much over that time, despite the disappointment. In this case, it seems that the EPS is guiding the share price.

The company's earnings per share (over time) is depicted in the image below (click to see the exact numbers).

It's probably worth noting that the CEO is paid less than the median at similar sized companies. But while CEO remuneration is always worth checking, the really important question is whether the company can grow earnings going forward. It might be well worthwhile taking a look at our free report on Canadian Solar's earnings, revenue and cash flow.

A Different Perspective

Investors in Canadian Solar had a tough year, with a total loss of 43%, against a market gain of about 12%. However, keep in mind that even the best stocks will sometimes underperform the market over a twelve month period. Unfortunately, last year's performance may indicate unresolved challenges, given that it was worse than the annualised loss of 8% over the last half decade. We realise that Baron Rothschild has said investors should "buy when there is blood on the streets", but we caution that investors should first be sure they are buying a high quality business. I find it very interesting to look at share price over the long term as a proxy for business performance. But to truly gain insight, we need to consider other information, too. Even so, be aware that Canadian Solar is showing 4 warning signs in our investment analysis , and 2 of those are concerning...

Of course, you might find a fantastic investment by looking elsewhere. So take a peek at this free list of companies we expect will grow earnings.

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.