U.S. Mac sales in October were down 16 percent year over year, according to the latest data from NPD Group. But Gene Munster of Piper Jaffray noted that Mac sales have exceeded NPD figures by an average of 12 percentage points in the last three quarters, which suggests, overall Mac sales were down just 4 percent year over year.
Munster's estimates call for Mac sales to be down 7 percent year over year in the December quarter, which would be 4.8 million total units.
The NPD figures suggest Mac sales were down 40 percent when compared to September. That's a normal seasonal trend as back-to-school sales end, Munster said.
"The focus of the December quarter will likely be on iPhone 5 sales, and we note our supply checks indicate that iPhone 5 supply has improved significantly in the last three weeks," he said.
This quarter will include sales of the new 13-inch MacBook Pro with Retina display, as well as new Mac minis with Ivy Bridge processors, and a redesigned iMac that is scheduled to arrive later this month. But Apple's Mac sales are dominated by portable machines, and the bulk of the company's MacBook lineup was refreshed earlier this year, while the latest updates feature more desktop machines.
A year ago, Apple set a new record by selling 5.2 million Macs in the December 2011 quarter. That represented a 26 percent increase from the same period in 2010.
Last year, Munster's interpretation of NPD's October sales data proved accurate in projecting Mac sales for the quarter. Munster said the sales figures showed Apple on pace to sell between 5.1 million and 5.3 million Macs in the quarter, and actual holiday Mac sales fell squarely in the middle of that range.