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: Shares of Rent-A-Center (Nasdaq: RCII) fell more than 11% on an analyst downgrade, kicked off by weak second-quarter results and lower full-year guidance.

So what: Stifel Nicolaus, a top-rated firm in our Motley Fool CAPS database, cut its rating from "buy" to "hold" after Rent-A-Center missed the Street consensus by $0.09 a share. Revenue came in light by about $2 million, The Associated Press reported.

Now what: Guidance really drove the sell-off. Rent-A-Center, which specializes in leasing household goods, revised its 2011 estimates down slightly. Management now expects $2.85 to $3 a share in earnings, on $2.87 to $2.91 billion in revenue. Previously, executives forecast $2.90 to $3.10 a share. Wall Street had been calling for $2.98 a share and $2.88 billion, respectively. Either way, hoped-for growth has gone missing -- and stock gains with it. Can management reverse the slide? Let us know using the comments box below.

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Fool contributorTim Beyers is a member of theMotley Fool Rule Breakers stock-picking team. He didn't own shares in any of the companies mentioned in this article at the time of publication. Check out Tim'sportfolio holdings andFoolish writings, or connect with him on Google+ or Twitter, where he goes by @milehighfool. You can also get his insightsdelivered directly to your RSS reader.

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