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 human resources specialist Insperity (NYSE:NSP) were falling sharply today, down as much as 16%, after its guidance missed in its earnings report.

So what: In the fourth quarter, Insperity beat EPS estimates by $0.02, with a $0.47 per-share profit, but fell short on revenue. Still, shares traded essentially flat until management provided guidance in the conference call, after which they fell 10% in just 20 minutes and continued sliding for the rest of the day. Management said it expected 2013 earnings to be just $1.47 to $1.56, due, in part, to reduced interest income, investment in health-care reform strategy, and a lower January starting point. Analysts had been expecting earnings of $1.66 a share.

Now what: With changes in payroll taxes and other work-related costs like health-care reform, Insperity seems headed for a more challenging 2013 than expected, but the overall business model still looks sound. The stock may still be pricy even after today's fall, but the long-term picture looks good for Insperity, especially as the job market improves.

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