Providing employees with 30in computer monitors can boost worker productivity at companies where 17in or 19in monitors are typically used, according to a French consultant hired for a study sponsored by Apple.

The study, which evaluated Apple's 30-inch Apple Cinema Display, concluded that large screens can offer gains of up to 50 per cent to 65 per cent in productivity on a variety of specific office tasks and can earn back their extra costs in time savings over several years. The 30-inch Apple Cinema Display costs £1,549.

But other experts say those conclusions are wrong, arguing that the productivity improvement estimates are too high and that using two monitors side by side would likely be a better productivity booster than one larger monitor. The 40-page study was conducted by Andreas Pfeiffer, principal of Paris-based Pfeiffer Consulting, for Apple, which paid for the research.

Pfeiffer looked at a range of computing tasks, from moving data between Word and Excel files to image manipulation using Photoshop. In addition to studying the 30-inch Apple display, Pfeiffer also did the comparison using a 17-inch Samsung SyncMaster 172x monitor. The Apple monitor has an optimal resolution of 2,560 pixels-x-1,600 pixels, compared with 1,280-x-1,024 pixels for the Samsung monitor.

The productivity gains, he said, occur because workers using larger monitors can avoid repetitive tasks such as switching between overlapping application windows. Instead, they can have more windows open side-by-side on a larger monitor.

The time savings are for commonly performed tasks and not meant to indicate overall productivity increases for workers, Pfeiffer said. Using a larger screen will only improve specific tasks where data is moved or manipulated quickly.

Pfeiffer's testing showed time savings of 13.63 seconds when moving files between folders using the larger screen - 15.7 seconds compared to 29.3 seconds on the 17in monitor - for a productivity gain of 46.45 per cent. The testing showed a 65.09 per cent productivity gain when dragging and dropping between images - a task that took 6.4 seconds on the larger monitor compared to 18.3 seconds using the smaller screen. And cutting and pasting cells from Excel spreadsheets resulted in a 51.31 per cent productivity gain - a task that took 20.7 seconds on the larger monitor versus 42.6 seconds on the smaller screen.

"There's a very, very clear and strong correlation between screen size and productivity," Pfeiffer said. "If you're used to a having a 15in or 17in laptop and then go to a smaller resolution laptop, you can realise [the difference]. There are certain things that can really slow you down."

A larger monitor is as important as higher resolution, which allows more of an image to be shown on the screen, he said. "Of course individual behaviour will impact productivity," he said. "A user who insists on using menus will be slower than one who uses keyboard shortcuts, for instance."

But several personal productivity experts who evaluate how hardware and work habits affect productivity disagreed with Pfeiffer's findings.

"I can surf the web on one monitor and do something else on the other," said Peggy Duncan, an Atlanta-based personal productivity expert and principal of PSC Press. "It all goes back to seeing more stuff at one time. But, in my opinion, productivity is increased more by using dual monitors."

Laura Stack, owner of The Productivity Pro consulting firm in Denver, said Pfeiffer's estimated productivity gains are way too high. She would estimate a maximum 5 per cent productivity gain for workers using a larger monitor. "But you're not going to see the boost in productivity you'll see by adding a second screen," which could increase productivity as much as 30 per cent, Stack said.

"People are not robots," Stack said. "It's impossible to see those kinds of productivity gains" as measured in the Pfeiffer study.

Neen James, a personal productivity expert who runs Neen James Communications, said a single larger screen could provide health benefits for workers such as less eye squinting, but she agreed that dual monitors would likely offer more verifiable productivity gains. "Those sorts of claims are fabulous from a marketing point of view," she said of the study, "but you can make statistics say anything."

Another productivity expert, however, said that either solution - a single large monitor or dual displays - could help workers, depending on what they do. "I think it would be a very personal decision," said Jan Jasper, principal of New York-based Jasper Productivity Solutions. "There's no contest to having more space to work."

Akilesh Bajaj, an MIS professor at the College of Business Administration at the University of Tulsa, reviewed the Pfeiffer report but said more research is needed before accurate conclusions are reached. "There's a lot of image processing [in the study] so it's easy to see where [the larger screen] would increase productivity," Bajaj said. But anecdotal remarks from colleagues estimated that they would not see substantial gains in their own work from having a larger screen, he said.

One multiple-monitor fan, Martin Doucet, owner of book-publishing company, Vaixe, said he uses one primary 19in CRT monitor and two additional 17in CRT monitors to get his work done more efficiently in his home office. Doucet said he has been using the system for two years, with one screen for manuscript proofreading, another to follow the author's story plan and the third for communicating via email or instant messaging.

"Having that much room makes it easy," he said. "I have everything at a glance. It saves time because you don't have to Alt-Tab all the time."

Apple's 30in display hasn't had much competition in that size range since its introduction, but Samsung will debut its own later this month, a company representative said.