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 athenahealth (Nasdaq: ATHN) fell 29% -- near a 52-week low -- on Thursday after spooking investors with poor guidance. The stock closed the day off 15%.

So what: The company, which sells technology for enabling electronic health records, told investors to expect $0.85 to $0.97 a share in 2012 earnings. Analysts were expecting $1.16 a share, according to data compiled by Yahoo! Finance.

Now what: Peers Quality Systems (Nasdaq: QSII) and Allscripts Healthcare (Nasdaq: MDRX) also fell, but marginally. Investors seem to think these rivals won't face the same sort of margin-bruising investment needs that athenahealth will navigate over the next year. Do you agree? Would you buy shares of athenahealth at current prices? Let us know what you think using the comments box below.

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This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.