It is almost impossible to see exactly the same numbers for different research companies, but they are usually very close. However, this is not what we have seen in recent studies of IDC and the Gartner on Mac sales in the US market during the fourth quarter of 2012.
The first said that Apple's numbers were down 0.2% compared to 2011 better than the PC industry in general, which fell 4.5%. According to them, Ma sold 2.03 million Macs in the period and, even with sales falling, it conquered the market (11.4%) thanks to the sharp decline of some competitors with the exception of HP and Lenovo, which grew relatively good.
J Gartner thinks Mac sales grew 5.4% in the period, with sales of 2.1 million, reaching 12.3% market share. According to them, the industry as a whole decreased by 2.1%.
Internationally, Apple did not figure in the top five manufacturers as usual and therefore was not mentioned. However, both IDC and Gartner expect positive numbers for the Cupertino firm we will know on 1/23, when Apple discloses its financial results.
Regardless of who is right, the low stocks of iMacs must have contributed to a performance here.
(via AppleInsider: 1, 2)