I found a reference to this article in my morning stroll through blogland: Multitasking makes you stupid, studies say.

The article, by Sue Shellenbarger of the WSJ, points to evidence that multitasking doesn’t really save time.

A growing body of scientific research shows that one of jugglers’ favorite time-saving techniques, multitasking, can actually make you less efficient and, well, stupider. Trying to do two or three things at once or in quick succession can take longer overall than doing them one at a time, and may leave you with reduced brainpower to perform each task.

“There’s scientific evidence that multitasking is extremely hard for somebody to do, and sometimes impossible,” says David Meyer, a psychology professor at the University of Michigan. Chronic high-stress multitasking also is linked to short-term-memory loss.

Yet we’re clearly engaged in a long-term trend toward doing more of it. Some 45 percent of U.S. workers feel they are asked or expected to work on too many tasks at once, says a study of 1,003 employees by the Families and Work Institute in New York.

The effect on knowledge workers is huge. Jerry Weinberg wrote on this topic in QSM 1, Systems Thinking (Dorset House, 1992).

# of tasks = 1 – Time spent on task = 100%

# of tasks = 2 – Time spent on task = 40%

# of tasks = 3 – Time spent on task = 20%

# of tasks = 4 – Time spent on task = 10%

# of tasks = 5 – Time spent on task = 5%

# of tasks = more than 5 – Time spent on task = random.

Notice that when someone is working on four tasks, he is spending 10% of his productive time on each task. That adds up to 40% of his time. Where does the other 60% go?

That missing 60% goes to:

–breaking concentration on the task A

–picking up task B

–organizing materials related to task B

–remembering where you were last time you worked on task B

–establishing concentration on task B

–overcoming emotional inertia

–recreating the train of thought that got you to the current point on task B….

and so forth and so on.

The cost can be higher if the level of tasks is different — going from high-level design work, for example, to detail coding.

Here’s what really surprised me about the current reporting on the cost of context-switching: it shows up in Work/Life balance pages. It should be on the business pages — as breakthrough thinking on improving worker productivity and driving down costs!