Optimal Pair Swapping: 90 minutes

Promiscuous Pairing and Beginner’s Mind: Embrace Inexperience "It often takes days for a given pair to be comfortable enough with each other to be able to achieve Pair Flow at all. This means that pairings tend to be long. The longer the mean time between pair swaps, the less effectively pair net distributes information through the team."

"While two people are paired, they share knowledge. When the pair splits for a pair swap, the knowledge then spreads to all four participants. In this way, knowledge will slowly but automatically spread around the group."

And the surprising result:
"This makes it easy to see the shape of the curve near the 90-minute optimal point. However, we did note that longer pair times had slightly higher mean velocities."

So you think you're doing extreme XP and someone always has to crank it up one more level. 90 minutes seems pretty close to me to be the minimum period of time to actually get a chunk of work done - considering that getting work done by yourself usually requires an hour.

I was actually looking for evidence that pair programming's flow state is better/worse than normal. Specifically,

• How much more or less is "pair flow" susceptible to interruptions,
• Whether pairs are able to resume, after interruption, more quickly into a shared flow state,
• Whether it's faster or slower to get into a "pair flow" state, and
• The effects experience has on the above.

Even Flow

"Flow is a mental state of operation in which the person is fully immersed in what he or she is doing, characterized by a feeling of energized focus, full involvement, and success in the process of the activity. Proposed by psychologist Mihaly Csikszentmihalyi, the concept has been widely referenced across a variety of fields."

Alister Cockburn's Team Per Task, "It takes about 20 minutes to reach this state of flow, and only a minute to lose it. Our designers found that it took about an hour to get into flow and make progress after having been stopped. If a meeting or other task arrived during this hour, the entire period was essentially lost. As it also took energy to get into the flow, a distraction cost but energy as well as time."

Pairing to to the rescue (again). When a pair gets into a flow it's more resilient to distractions - it seems to allow one person in the pair to get back into it more quickly after being distracted. Maybe it is related to mirror neurons (video).