Advertisers spend three times as much targeting Apple devices as Android ones, according to a new study — a stat even the most devoted iPhone users wouldn’t brag about.

The iPhone monthly ad share grew 12% in the first quarter of this year and now accounts for more than 50% of mobile ad spending, according to the report released Thursday by MoPub, a mobile ad exchange that allows app publishers and advertisers to engage in bidding for advertisements. As a result, the cost-per-thousand views is 40% higher on iOS than Google’s GOOG, -2.25% Android.

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Why are Apple AAPL, -1.67% users bombarded with more ads than those who own rival devices are? Experts say the user base is considered a more upwardly mobile demographic. “Apple has more desirable customers,” says Sarah Rotman Epps, senior analyst at Forrester Research. Cheaper Android phones reach more people than the iPhone, she says, but around 15% of Samsung 005930, -2.45% smartphone customers get free Android smartphones that come with wireless contracts. “These accidental customers are in the lower third of income earners in the U.S.,” she says. “They’re not necessarily the customers that advertisers care most about reaching.”

Research appears to support that thesis. Apple gadgets had a click-through rate of 1.7% in March – 1.7% for the iPhone and 2.5% for the iPad — compared with 1.1% for Android phones and tablets, MoPub found. iPad users also typically spend more at ecommerce sites than other tablet users: They spend $158 per order — the highest of any device – compared with $105 by people on other mobile devices, according to a separate study by RichRelevance, a personalized product recommendation company.

Reuters

But the ad growth presents a challenge for Apple, which works hard to ensure that the user experience is not greatly diminished while people download apps, clicking on an ad, or buy books or music, says technology analyst Jeff Kagan. “Right now, Apple does a better job of placing appropriate ads in the right places,” he says. (Apple didn’t respond to requests for comment.)

These mobile ads are also ramped up during big events like March Madness, “creating a sudden and dramatic spike” in ad spending MoPub.com found. “Mobile media buyers opportunistically shifted ad spend in real time based on insights about user behavior during severe weather storms, holidays and live mass media events,” the report said. Conversely, they pulled back on ads ahead of the “fiscal cliff” — the series of tax and budgetary measures that were due to expire at the end of last year.