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 retailer Express (Nasdaq: EXPR) were looking pretty unfashionable today as investors knocked them down 13% after the company's earnings announcement.

So what: The numbers from the first quarter actually looked pretty good. Comparable store sales growth of 8% drove a 10% increase in overall revenue, while operating income jumped 35% as the company's operating margin expanded from 12% to 14.9%. Sales of $467 million and adjusted earnings per share of $0.42 topped the respective average analyst estimates of $459 million and $0.40.

Now what: Obviously investors were reacting to something other than the first-quarter results, and that something may be the company's guidance. Management projected second-quarter EPS to be in a range of $0.12 to $0.15, while full-year EPS will likely be between $1.52 and $1.61. The full-year range is actually a slight increase from the last projection that the company offered, but it appears it wasn't enough to appease investors. Wall Street's estimates for the quarter and full year were $0.16 and $1.58, respectively.

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