If you want to compound wealth in the stock market, you can do so by buying an index fund. But you can do a lot better than that by buying good quality businesses for attractive prices. For example, the Energy Recovery, Inc. (NASDAQ:ERII) share price is up 99% in the last five years, slightly above the market return. In stark contrast, the stock price has actually fallen 34% in the last year.

The past week has proven to be lucrative for Energy Recovery investors, so let's see if fundamentals drove the company's five-year performance.

Check out our latest analysis for Energy Recovery

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 five years of share price growth, Energy Recovery achieved compound earnings per share (EPS) growth of 7.5% per year. This EPS growth is lower than the 15% average annual increase in the share price. So it's fair to assume the market has a higher opinion of the business than it did five years ago. And that's hardly shocking given the track record of growth. This favorable sentiment is reflected in its (fairly optimistic) P/E ratio of 51.04.

You can see how EPS has changed over time in the image below (click on the chart to see the exact values).

We like that insiders have been buying shares in the last twelve months. Having said that, most people consider earnings and revenue growth trends to be a more meaningful guide to the business. It might be well worthwhile taking a look at our free report on Energy Recovery's earnings, revenue and cash flow.

A Different Perspective

Energy Recovery shareholders are down 34% for the year, but the market itself is up 27%. Even the share prices of good stocks drop sometimes, but we want to see improvements in the fundamental metrics of a business, before getting too interested. Longer term investors wouldn't be so upset, since they would have made 15%, 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. It's always interesting to track share price performance over the longer term. But to understand Energy Recovery better, we need to consider many other factors. Consider for instance, the ever-present spectre of investment risk. We've identified 2 warning signs with Energy Recovery , and understanding them should be part of your investment process.

There are plenty of other companies that have insiders buying up shares. You probably do not want to miss this free list of undervalued small cap companies 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.