With a price-to-earnings (or "P/E") ratio of 8.4x Pfizer Inc. (NYSE:PFE) may be sending bullish signals at the moment, given that almost half of all companies in the United States have P/E ratios greater than 14x and even P/E's higher than 27x are not unusual. Although, it's not wise to just take the P/E at face value as there may be an explanation why it's limited.

With earnings growth that's superior to most other companies of late, Pfizer has been doing relatively well. One possibility is that the P/E is low because investors think this strong earnings performance might be less impressive moving forward. If not, then existing shareholders have reason to be quite optimistic about the future direction of the share price.

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Does Growth Match The Low P/E?

In order to justify its P/E ratio, Pfizer would need to produce sluggish growth that's trailing the market.

If we review the last year of earnings growth, the company posted a terrific increase of 140%. Pleasingly, EPS has also lifted 138% in aggregate from three years ago, thanks to the last 12 months of growth. So we can start by confirming that the company has done a great job of growing earnings over that time.

Turning to the outlook, the next three years should bring diminished returns, with earnings decreasing 14% each year as estimated by the analysts watching the company. With the market predicted to deliver 9.6% growth per annum, that's a disappointing outcome.

In light of this, it's understandable that Pfizer's P/E would sit below the majority of other companies. Nonetheless, there's no guarantee the P/E has reached a floor yet with earnings going in reverse. Even just maintaining these prices could be difficult to achieve as the weak outlook is weighing down the shares.

What We Can Learn From Pfizer's P/E?

While the price-to-earnings ratio shouldn't be the defining factor in whether you buy a stock or not, it's quite a capable barometer of earnings expectations.

We've established that Pfizer maintains its low P/E on the weakness of its forecast for sliding earnings, as expected. Right now shareholders are accepting the low P/E as they concede future earnings probably won't provide any pleasant surprises. Unless these conditions improve, they will continue to form a barrier for the share price around these levels.

You should always think about risks. Case in point, we've spotted 1 warning sign for Pfizer you should be aware of.