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 insurance company Tower Group (Nasdaq: TWGP) fell 13% this morning after the company released earnings.

So what: Earnings per share jumped nicely to $0.92 from $0.72 a year ago and easily topped the $0.83 analysts expected. But it was outlook that investors are focused on today. The company expects 2011 earnings per share of $2.70 to $2.90 per share, but analysts had set their sights on $3.46 per share.

Now what: The fourth-quarter earnings beat is welcome news, but it looks like analysts had gotten ahead of themselves with expectations for 2011. Management said it expected challenging conditions to continue in 2011 and expected lower returns on its investment portfolio. It looks like management wants to overpromise and underdeliver, and considering the big drop today, I see this as a nice buying opportunity.

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