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 polymer specialist PolyOne (NYSE: POL) jumped as much as 11% in intraday trading as investors cheered an upgrade from a Wall Street analyst.

So what: KeyBanc Capital Markets analyst Michael Sison gave investors the green light on PolyOne shares, upgrading the stock from hold to buy. The driver for the upgrade was a company restructuring that may be wrapping up and leading to a new growth phase for PolyOne. Sison sees earnings-per-share growth in the "mid to high teens" in the coming years and put a price target of $18 on the stock.

Now what: A recommendation from a Wall Street analyst may be more reliable than that of Uncle Bob who got a "hot tip" from some unknown source, but it's still best for investors to do their own work to make sure the investment really measures up. In the case of PolyOne, the KeyBanc upgrade could be a good reason to take a look at the stock -- or a second look -- but Foolish investors should make sure they have a lot more to go on than one Wall Street upgrade.

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Fool contributor Matt Koppenheffer does not own shares of any of the companies mentioned. You can check out what Matt is keeping an eye on by visiting his CAPS portfolio, or you can follow Matt on Twitter @KoppTheFool or on his RSS feed. The Fool's disclosure policy is looking forward to a great 2011!