Tablet shipments surged 75% last quarter. Apple’s iPad still dominant, but less so by Philip Elmer-DeWitt @FortuneMagazine January 31, 2013, 12:34 PM EST E-mail Tweet Facebook Google Plus Linkedin Share icons Take with a grain of salt. FORTUNE — IDC on Wednesday released preliminary data from its survey of worldwide tablet sales in the big holiday quarter, and the only thing in the data that we can be sure about is that sales of Apple’s iPad grew 48.1% year over year — from 15.1 million to 22.9 million. We and IDC know this because Apple AAPL reported those unit sales figures last week. The rest of IDC’s report is almost entirely guesswork. It says that Samsung shipped 7.9 million tablets — up 263% — but doesn’t say how it got those numbers. Certainly not from Samsung, which hasn’t released unit sales figures for any of its devices in years. IDC also says that Amazon AMZN shipped 6 million Kindles — up 26.8%. This despite the fact that Amazon has never once said how many Kindles it sold, a policy that remained conspicuously in force during Tuesday’s Q4 2012 earnings call. As for the rest of IDC’s findings, they just get more bizarre. The press release says Barnes & Noble BKS “gained traction” in the tablet market, but the spreadsheet shows Nook sales falling year over year. Even more startling, the release says Asus lost share, while the spreadsheet shows Asus’ market share nearly tripling on sales that grew 402.5%. Given the level of guesswork and sloppy reporting we see here, you should probably take the specificity of headlines like this … IDC: Apple’s iPad dropped to 43.6% tablet share in Q4, Samsung took second with 15.1%, Amazon third with 11.5% with, as they say, a grain of salt. IDC’s spreadsheet below: Click to enlarge.