Undocumented Features

The Limits to Multitasking: How Divided Are Your Resources?

October 22, 2007 – 4:38 pm

It’s a fairly common practice to share resources in a company for projects.  A single systems engineer, for example, may be assigned to work with three or four different projects.  As long as the total number of hours that the various projects are asking for matches up to the total number of hours that the engineer is available, this is usually looked at as acceptable.  After all, the numbers don’t lie; the engineer has sufficient time available, right?

As you have probably experienced, this is almost never the case.  The numbers say the engineer has time; he never actually does.  We usually blame this on poor estimates.  I propose that it’s something else that we sometimes forget:  the limits to multitasking. 

Research has shown that humans are not particularly good at switching contexts.  People like Gerald Weinberg and others have done much research to prove it.  The commonly accepted table for this is below:

(original version of this graph shown here, where Coding Horrors also writes on this topic).

What does this mean to you?  Should you stop having people multitask?  That is not realistic in most business models.  If you have a task that requires 20 hours a week, then a 40-hour a week employee needs something else to do all week.  What you need to do is keep up with how people’s time is distributed, and allow for the multitasking factor.  If a person is on 2 projects, then 20% of their time will be consumed by changing gears between.  If they’re three projects, it will consume 40%, and so on.  Adjust your schedule accordingly, and talk to their managers if you foresee problems.

And if you have to, share this article with them to help them see your point.

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