For example, can Apple continue to sell in China without sacrificing profit? Sterne Agee CRT analyst Rob Cihra estimates that the world's second-biggest economy accounted for 25 percent of iPhones sold in 2015 and 43 percent of Apple's growth.
In China, "Apple proved it could grow last year through share gains in an otherwise down market, but macro headwinds continue," wrote Cihra, who has a buy rating on the stock and a $160 price target. The shares have dropped 8.5 percent in January to close Thursday at $96.30.
Facebook and Alphabet are counting on businesses to continue their ad spending even as budgets tighten. Considering the ongoing shift from offline to online marketing and the greater efficiency tied to Internet and mobile advertising, the top Web companies may be best positioned to weather any decline.
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According to a September report from eMarketer, Google's share of U.S. digital advertising will slip to 37.4 percent this year from 40.1 percent in 2015, while Facebook's will increase to 14.7 percent from 13.2 percent. No other company tops 5 percent.
"The apparent acceleration in retail spending allocation to online outlets and anecdotes from the advertising community make us think that ad dollar shift from traditional media to Internet will surprise in Q4, as it did a year ago," wrote MKM Partners analyst Rob Sanderson, who has buy ratings on Facebook and Alphabet. "FB is in the best position to benefit and we think likely to take more than its share of incremental ad dollars."
Alphabet faces the added challenge of breaking out its nonadvertising businesses for the first time. The Google search, display and mobile ad business accounts for all the profit, while investors will now get to see just how much the parent company is spending on initiatives like autonomous cars and extending life.