Here are a pair of headline shockers:

• AppleInsider: iOS dominates mobile shopping with 92% of market
• Forbes: iOS Took 13.4% of Online Sales on Christmas Day

Both stories got pretty big play over the Christmas break. But they can’t both be right, can they? Let’s look at the facts.

The 92% figure comes from a Dec. 21 report by a San Francisco-base company called RichRelevance that monitors the browsing patterns of online shoppers at sites like Walmart.com and recommends similar products. It analyzed at a lot of shopping sessions — 3.4 billion between April and December — and noted several trends:

• The share of retail dollars from online shopping hit 3.74% in December, up from 1.87% in April
• The share of online shopping sessions from mobile devices more than doubled — to 18% from under 9% — in that 9-month period
• Apple (AAPL) iOS devices accounted for 92% of sales from those mobile devices in December, up from 88% in April.

In other words, 92% of 18% of a tiny sliver (3.74%) of total online sales in the three weeks leading up to Christmas came from iOS devices. Not quite as impressive as the original headline suggested.

The second report comes from an IBM study of online sales at some 500 sites for one day in December — Christmas Day, after most of the presents had presumably already been opened and a lot of gift cards received. It found, according to
Forbes
, that:

• Online sales grew by 16.4% over Christmas Day 2010
• Mobile devices accounted for 14.4% of those online sales, up 172.9% year over year
• 7% were made from iPads
• 6.4% were made from iPhones
• 5% were made from Google (GOOG) Android devices

That makes a bit more sense. Although the two reports studied different periods (one the walk-up to Christmas, the other the aftermath on Christmas Day), the results were a lot more alike than they seemed at first. RichRelevance found that 16.6% (92% of 18%) of online sales were made from iOS devices. IBM’s number was 14.3%.

Not that different. And not too shabby. As IBM’s John Squire put it:

“The iPad wasn’t even around two years ago and now it’s the leading mobile device for purchases. Android came out from nowhere last year, and now it is in third place.”