But the results could be at -2% in the IDC report because Apple's actual forth quarter of 2022 was up on Macs by 30% but down 30% in their 1st quarter of 2023. So the estimate seems pretty close if IDC is splitting those quarters.
I still have difficulty wrapping my head around these figures. Let's have a look at it again and try to figure out what's going on.
Per IDC report, Mac Sales went down 2% in Q4 2022 and 40% in Q1 2023. They do not specify the actual date range behind these quarters, but since it's a table with multiple vendors and the results were always released the next calendar month, it makes sense to assume that these are calendar quarters. So, again, according to IDC we have 2% decrease in Mac sales from October-December 2022 and 40% from January-March 2023 (compared to the same period the previous year).
Now, according to Apple's financial report they have lost 40% in Mac revenue in October-December 2022 compared to October-December 2021. This makes sense, since there were no product releases in that quarter, while the 2021 quarter had new MacBook Pros. What I still don't understand how 40% in revenue loss translates to 2% fewer sales reported by IDC. Even if what you say is correct that they went up one quarter and then down next quarter, it still doesn't add up, unless IDC's quarter crosses the calendar year (which would be the weirdest definition of quarter ever).
We will see in May, when Apple releases the financial data for the first calendar quarter of 2023. In the meantime I have a suspicion that IDC personnel did a mistake aggregating the data and confused the fiscal quarters and calendar quarters.