Dr. Jakob Nielsen, world renown expert on usability, has gotten fed up with the coverage of Apple's "study" saying that larger monitors increase productivity (PDF). He doesn't have anything against large monitors per se, but he says that Apple's methodology for performing such a "study" is way out of whack with what is normally done during a usability study:
A prominent article about Apple's study reports, for example, that "cutting and pasting cells from Excel spreadsheets resulted in a 51.31% productivity gain — a task that took 20.7 seconds on the larger monitor versus 42.6 seconds on the smaller screen."
Apple's study focused at the wrong level of work. Pasting spreadsheet cells is not a user task, it's an operation at a low interaction level. More meaningful productivity has to be measured at a higher level, where users string together a sequence of operations to achieve their real-world goals.
Indeed, when I was in college and was tasked with performing a usability study on 3D software, we weren't allowed to tell our subjects to just do one task (move the ball from here to here on the screen) and see how good they performed at it. We told them to animate a ball bouncing by using any and all tools available to them in the software, or any other software on the computer for that matter, and measured their ability to get the job done in a string of unspecified tasks.
The distinction between operations and tasks is important in application design because the goal is to optimize the user interface for task performance, rather than sub-optimize it for individual operations.
Nielsen also criticizes Apple for testing users using "rote, low-level operations that they'd trained on repeatedly until they got them exactly right," making them very skilled at the tasks they were being tested in instead of testing users based on realistic use. Extremely skilled performance is not something that happens a majority of the time for anyone using the computer, he says.
Skilled performance almost never happens on the Web, because users constantly encounter new pages; that is, they spend most of their time pondering options and trying to understand the content that's being presented.
Even in applications, skilled performance is rare because modern office workers typically move between many different tasks and screens.
So how would he have conducted the study?
-Involve a broad spectrum of representative users (not just experts).
-Have the users perform representative tasks (not just a few low-level operations).
-Don't tell users how to do the tasks; observe their real behavior.
Don't mess with Jakob Nielsen. It seems that the Apple study made a number of mistakes that even undergraduate students in usability classes (*ahem*) are taught not to do when conducting usability studies. Did they do it all for marketing purposes, so that they could sell more gigantic 30-inch monitors? Probably. However, maybe if they consulted a few experts and did it "right," the result may have been the same and they could still sell plenty of those gigantic 30-inchers.