Stanford University is in the middle of a formal experiment on Pair Programming. I participated in the experiment this past weekend and had a lot of fun and, hopefully, helped advanced the state of knowledge about this controversial software development technique.
A PDF document describing the experiment is available at http://hci.stanford.edu/research/pairs/PairProgramming-WhenWhy.pdf
The experiment is currently in the second ("Laboratory Experiment") phase as described in that document.
In the first phase ("Ethnographic Field Study") of the experiment the researchers visited two companies where pair-programming is regularly practiced and observed and recorded audio of programming pairs. These observations helped the researchers develop some hypothesis which may be checked by further work in the experiment.
The researchers are focusing on the interaction between the people in the pairs (the "socio-cognitive factors" is how they say it.) The current phase of the experiment involves controlled tests where a pair of programmers or a solo programmer complete a warmup task and then a larger task (which takes around 5-6 hours all together.) The programmers are recorded via audio, video, and screen captures.
During my pairing session this past weekend we talked a bit about the notion that once we humans have a goal we often have a strong impulse to start acting towards that goal, without necessarily doing much planning or testing - like driving nails before deciding where, exactly to drive the nails, and that we continue with our actions without doing much checking if we are in fact heading towards our goal. I don't think that Pair Programming stops individuals from having this impulse, but the presence of a second person makes it more likely, perhaps, that someone else will stop us. Hence my new joking slogan: "Pair Programming: It's not twice as smart, it's half as dumb!"
Pair Programming as a formally recognized technique has been around for over a decade now, and as an informal reality I would guess it has been around for as long as there has programming. There has been only a little formal study of Pair Programming though, and Pair Programming is perhaps the most controversial technique in the eXtreme Programming methodology, touching as it does directly on people's self-image and personalities.
I hope this experiment will help advance the state of knowledge about software development in general, and Pair Programming in particular, so that we can make better decisions about how to build things.
The experiment is led by Robert P. Plummer, PhD., a Lecturer in the Stanford Department of Computer Science. Inquiries about the experiment can be sent to experiment at cs.stanford.edu.