Time to Sell InterDigital?

Should you sell InterDigital (Nasdaq: IDCC) today?

The decision to sell a stock you've researched and followed for months or years is never easy. If you fall in love with your stock holdings, you risk becoming vulnerable to confirmation bias -- listening only to information that supports your theories, and rejecting any contradictions.

In 2004, longtime Fool Bill Mann called confirmation bias one of the most dangerous components of investing. This warning has helped my own personal investing throughout the Great Recession. Now, I want to help you identify potential sell signs on popular stocks within our 4-million-strong Fool.com community.

Today I'm laser-focused on InterDigital, ready to evaluate its price, valuation, margins, and liquidity. Let's get started!

Don't sell on price
Over the past 12 months, InterDigital has risen 32.1% versus an S&P 500 return of 11.3%. Investors in InterDigital have every reason to be proud of their returns, but is it time to take some off the top? Not necessarily. Short-term outperformance alone is not a sell sign. The market may be just beginning to realize the true, intrinsic value of InterDigital. For historical context, let's compare InterDigital's recent price to its 52-week and five-year highs. I've also included a few other businesses in the same or related industries:

Source: Capital IQ, a division of Standard & Poor's.

InterDigital is basically at its 52-week high. This means we need to dig into the valuation to ensure that these previously new highs are justified.

Potential sell signs
First up, we'll get a rough idea of InterDigital's valuation. I'm comparing InterDigital's recent P/E ratio of 8.4 to where it's been over the past five years.

Source: Capital IQ, a division of Standard & Poor's.

InterDigital's P/E is significantly lower than its five-year average, which could indicate the stock is undervalued. A low P/E isn't always a good sign, since the market may be lowering its valuation of the company because of less attractive growth prospects. It does indicate that, on a purely historical basis, InterDigital looks cheap.

Now, let's look at the gross margins trend, which represents the amount of profit a company makes for each $1 in sales, after deducting all costs directly related to that sale. A deteriorating gross margin over time can indicate that competition has forced the company to lower prices, that it can't control costs, or that its whole industry's facing tough times. Here is InterDigital's gross margin over the past five years:

Source: Capital IQ, a division of Standard & Poor's.

InterDigital is having no trouble maintaining its gross margin, which tends to dictate a company's overall profitability. This is solid news; however, InterDigital investors need to keep an eye on this over the coming quarters. If margins begin to dip, you'll want to know why.

Next, let's explore what other investors think about InterDigital. We love the contrarian view here at Fool.com, but we don't mind cheating off of our neighbors every once in a while. For this, we'll examine two metrics: Motley Fool CAPS ratings and short interest. The former tells us how Fool.com's 170,000-strong community of individual analysts rate the stock. The latter shows what proportion of investors are betting that the stock will fall. I'm including other peer companies once again for context.

Source: Capital IQ, a division of Standard & Poor's.

The Fool community is rather bullish on InterDigital. We typically like to see our stocks rated at four or five stars. Anything below that is a less-than-bullish indicator. I highly recommend you visit InterDigital's stock pitch page to see the verbatim reasons behind the ratings.

Here, short interest is at a high 14.9%. This typically indicates that large institutional investors are betting against the stock.

Now, let's study InterDigital's debt situation, with a little help from the debt-to-equity ratio. This metric tells us how much debt the company's taken on, relative to its overall capital structure.

Source: Capital IQ, a division of Standard & Poor's.

InterDigital has taken on basically no debt over the past five years, which gives them a basically irrelevant debt-to-equity ratio. Normally I view ratios over 50% as a warning sign.

The last metric I like to look at is the current ratio, which lets investors judge a company's short-term liquidity. If InterDigital had to convert its current assets to cash in one year, how many times over could the company cover its liabilities? As of the last filing, InterDigital has a current ratio of 2.86. This is a healthy sign. I like to see companies with current ratios greater than 1.5.

Finally, it's highly beneficial to determine whether InterDigital belongs in your portfolio -- and to know how many similar businesses already occupy your stable of investments. If you haven't already, be sure to put your tickers into Fool.com's free portfolio tracker, My Watchlist. You can get started right away by clicking here to add InterDigital.

The final recap

InterDigital has failed only two of the quick tests that would make it a sell. This is great, but does it mean you should hold your InterDigital shares? Not necessarily. Just keep your eye on these trends over the coming quarters.

Remember to add InterDigital to My Watchlist  to help you keep track of all our coverage of the company on Fool.com.

If you haven't had a chance yet, but sure to read this article detailing how I missed out on over $100,000 in gains through wrong-headed selling.