If you’re working on three projects, you’re probably spending 40% of your time task switching. Task switching is the dark matter of life: there’s a lot of it, but we’re hardly aware of it.
I’m not talking about multitasking, such as replying to email while you’re on the phone. People are starting to realize that multitasking isn’t as productive as it seems. I’m talking about having multiple assignments at work.
John Maeda posted a note about multiple projects in which he gives a link to a PowerPoint slide graphing percentage of productive time as a function the number of concurrent assignments. According to the graph, the optimal number of projects is two. With two projects, you can do something else when one project is stuck waiting for input or when you need variety. But any more than that and productivity tanks.
Johanna Rothman has an interview on the Pragmatic Programmer podcast where she discusses, among other things, having multiple concurrent projects. She thought it was absurd when she was asked to work 50% on one project, 30% on another, and 20% on another. Research environments are worse. Because of grant funding, people are sometimes allocated 37% to this project, 5% to that project, etc.
We’re not nearly as good at task switching as we think we are. I hear people talking about how it may take 15 or 30 minutes to get back into the flow after an interruption. Maybe that’s true if you were interrupted from something simple. A colleague who works on complex statistical problems says it takes her about two or three days to recover from switching projects. In his article Good and Bad Procrastination, Paul Graham says “You probably only have to interrupt someone a couple times a day before they’re unable to work on hard problems at all.”