Wednesday, July 29, 2009

Interruption and the Cost of Context Switching

I've been thinking about interruption lately. I shared some thoughts about anticipating interruptions in an article about the probability of interruption. More obviously, when an interruption happens it costs me something. Specifically, I have to switch from doing one thing to doing something else. There's a non-zero cost to focusing my mind on a new task. That effort is pure overhead. It's like energy lost to friction or electricity spent "heating the whole neighborhood" (as our parents used to say). If one can reduce interruptions, one should be able to reduce context switching costs.

I use a small program that I wrote to record the time I spend working. When I switch tasks, I press a few keys to indicate what I'm working on now. At the end of the month, I use this data to generate invoices, etc. Even though I don't record every context switch in my time clock program, I do record many of them. Reviewing the data for the last 18 months shows that I worked on 1,635 unique tasks. I switched context 7,768 times (subjectively, most of those were caused by interruptions). On average, I spent 25 minutes working on a given task before switching to something else. If I assume it takes me two minutes after a context switch to become productive again (which is a very conservative estimate), it means that I spent 7% of my total working time just switching between responsibilities. That 7% produced very little value for me or my clients.

Managing interruptions is an important component of enhancing one's productivity. I'd be thrilled if I could effectively have 7% more time in a day.

1 comment:

TanookiTravis said...

It's crazy to me that 7% of your time is spent switching contexts from one to another. I can only imagine if major companies thought this threw most employees would have walled cubes.