In today’s workplace, multitasking is appreciated by many as a good work habit and a sign of commitment to the job. Some people seem to be able to juggle personal crises, help co-workers and still get their work done. While they may whirl like dervishes, they seem to take it all in stride without breaking a sweat. These people are powerhouses of productivity—or does it just seem that way?
Former Secretary of State, Henry Kissinger, was considered by some to be as powerful as the president during his time in office, and yet he often missed key meetings or ran late. When he did arrive, he invariably stepped out to make at least one telephone call during the meeting. In retrospect, his tenure at the State Department was one of the least productive in recent history, despite his political power and academic prowess. 
The Cult of Busy
Chronic multitaskers often comment about how busy they are all the time and how much they still have to do. Somehow though, come the end of the week, they seem to have just as much on their to-do lists as they did the start of the week. The cult of busy can quickly become all encompassing. It can even begin to serve as validation, since being constantly busy and keeping multiple balls in the air is what makes an employee indispensable—right?
That might be true if multitasking enhanced productivity without impacting quality; if multitasking didn’t have
“a negative physical effect, prompting the release of stress hormones and adrenaline.[That can] trigger a vicious cycle, where we work hard at multi-tasking, take longer to get things done, then feel stressed, harried and compelled to multi-task more.”
Multitaskers Are Lousy at Multitasking
A 2009 study by three Stanford University researchers found that cognitive control, the ability to make decisions (known as executive function), memory, and the skill to implement a task with as few mistakes as possible, was worst for self-proclaimed multitaskers. Jim Taylor, an adjunct psychology professor at the University of San Francisco, describes the pervasive endorsement of multitasking as “a myth promulgated by the ‘technological-industrial complex’ to make overly scheduled and stressed-out people feel productive and efficient.”
According to Taylor, what we think of as a fast drive down the information superhighway is really us “stepping on the gas then hitting the brakes, over and over.” And getting nowhere fast!
This effect happens because the brain unavoidably retains information about the previous task when it shifts gear into the next one; thus leaving the previous task mentally unfinished. As a result, the subsequent task is shortchanged on brain power, and the next one gets even less attention. The more we multitask, the more cumulative the brain drain. In fact, Clifford Nass, one of the authors of the Stanford study, said they found “that [high multitaskers] are lousy at everything that's necessary for multitasking.”
Bottom Line Impact of Multitasking
A comprehensive study of 45 organizations, with over $1 billion each in annual revenues, found that multitasking “cost the global economy more than $450 billion in lost productivity.”
This massive productivity loss comes from the fact that multitaskers experience a 40% drop in productivity, take 50% longer to complete a task, and make more mistakes. University of London researchers found that chronic multitasking can also temporarily lower IQ by up to 15 points, which is three times more than the effect of frequent cannabis use. In spite of these negative impacts, it seems the addictive buzz that some people get from juggling many important tasks might have something to do with why people persistently multitask. For others, multitasking is considered a necessary evil, not a preference, and they bear the cumulative stress in silence rather than admit they are desperate for uninterrupted focus time.
Whatever we may believe about the power of multitasking, research shows that a combination of task prioritization and focus is a much better use of our time (and our brains). Focusing completely on one task at a time, rather than flipping between tasks or trying to do two or more things at once, makes us more productive, more accurate and less stressed out.
 Walter Isaacson, Kissinger: A Biography (Simon & Schuster, reissued, 2005), p. 142
 Conducted by Realization, a flow-based project management software firm. http://www.realization.com/pdf/Effects_of_Multitasking_on_Organizations.pdf