What: LinkedIn (NYSE:LNKD) shares were crushed on Friday, following the company's fourth-quarter earnings release on Thursday after market close. A worse-than-expected forecast for the first quarter and full year may be a key reason for the sell-off.

So what: Fourth-quarter results were actually better than expected. LinkedIn reported revenue of $862 million and non-GAAP EPS of $0.94. These results represent 34% and 54% year-over-year growth, respectively. The average analyst expectation for revenue and non-GAAP EPS for the quarter was $857 million and $0.78, respectively, according to Reuters. 

But the company's guidance for its first quarter and the full year was much worse than analysts expected. For the first quarter, analysts had forecasted about $867 million and $0.74 in revenue and non-GAAP EPS, respectively. These expectations turned out to be well above LinkedIn's Q1 guidance for revenue and non-GAAP EPS of $820 million and $0.55, respectively. For the full year, analysts anticipated revenue of about $3.91 billion, and LinkedIn guided for full-year revenue of $3.6 billion to $3.65 billion.

Now what: Guidance for decelerating growth in 2016 -- down from about 35% year-over-year growth in 2015 to growth around mid-20% in 2016 -- reflects a number of factors, including expectations for further economic headwinds in its EMEA and APAC geographic segments, some impact from "tough comparisons," and 2% negative impact from unfavorable currency headwinds, as management explained during the company's prepared remarks for the earnings call. Revenue in the back half of the year will also be negatively affected by about $50 million as the company factors in the removal of potential Bizo revenue due to management's decision to end a product that "required more resources than anticipated to scale."

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