When we talk about enemies of productivity, multitasking is near the top of the list. Once thought to be a superpower, the generally-accepted principle now is that multitasking is a bad thing. People who multitask aren’t doing two things equally well. They’re doing two things equally poorly.

A 2005 study in Great Britain found that the multitasking involving constantly going back and forth between email and some other task caused a short-term reduction in IQ:

In 80 clinical trials, Dr. Glenn Wilson, a psychiatrist at King’s College London University, monitored the IQ of workers throughout the day. He found the IQ of those who tried to juggle messages and work fell by 10 points — the equivalent to missing a whole night’s sleep and more than double the 4-point fall seen after smoking marijuana.

Why is multitasking so bad?

What we’ve found is that what we call “multitasking” is really rapidly shifting focus from one thing to another. That shifting of focus brings with it lost motion. Every task involves some “start-up” time. The more we shift focus, the more we have to go through that “start-up” routine.

We never get in what psychologists call “flow.” When we’re in a state of flow, mistakes are minimized and concentration is at a maximum.

“Good multitasking”: the secret

The attraction of multitasking is the supposed ability to do two (or more) things at the same time. The idea is to get more done in the same amount of time.

For example, when I ride the treadmill, I watch TV shows I have recorded. Neither activity requires mental effort. Walking is good exercise. I’m able to watch TV without it taking time from other activities. Some people run while listening to podcasts. That’s another good example.

While the dogs are eating their food, I’m loading (or unloading the dishwasher) for as long as it takes them to eat. If I don’t finish, I continue when I am heating a cup of coffee later in the day.

I have the “next read” at hand. Whether it’s a book or a magazine, when I find myself with wait time, I can read. After all, “waiting” requires little concentration. Of course, making this idea work means making a decision about that next read and putting it in my briefcase or inbox. When the appropriate time presents itself, the decision as to what to read has already been made.

Closely related, I subscribe to certain blogs. All new content from them goes to one place. While I am in line at the grocery store or waiting to pick up a to-go order, my phone houses those things I told myself I wanted to read anyway.

In this post, I talked about preparing all birthday cards for the year while watching television. Applying stickers to envelopes doesn’t exactly require a great deal of attention.

Even preparing a draft of this blog post is an example of good multitasking. I have a note in Evernote for each post coming up for the next month. As I think about a point I want to make, I add it to the note.

Now it’s your turn. What are some pairs of tasks you could do at the same time? I would welcome your ideas.