Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Rent-A-Center (Nasdaq: RCII) shares are in freefall today -- one of the biggest losers on the Street -- and I'll bet you can guess why. It is, after all, earnings season. And when a stock takes a 12% tumble during earnings season, chances are the reason it's falling is because it missed earnings. And Rent-A-Center missed big-time.

So what: The question is how big? Analysts say they were looking for $0.85 per share this quarter, and Rent-A-Center says it earned $0.79 -- which doesn't sound too bad. Then again, RAC's number was of the pro forma variety; under GAAP accounting standards, the company was forced to admit it only earned $0.69.

Now what: Interestingly, RAC rival Aaron's (NYSE: AAN) also reported earnings yesterday, but with opposite results, beating estimates handily with a $0.55-per-share profit -- up 20% year over year. As Aaron's CEO Robert Loudermilk stated at the time, "The numbers speak for themselves." I agree. And what the numbers are saying is that Aaron's is beating the pants off Rent-A-Center.

This being the case, if you're looking at Rent-A-Center today, and thinking the stock looks attractive at 11.6 times earnings, with 11.8% growth in the future ... think again. This stock may not be as cheap as it looks.

Think Rent-A-Center is one to own? Add it to your watchlist and find out.

Fool contributor Rich Smith does not own (or short) Rent-A-Center. The Motley Fool has a disclosure policy. Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors.