Re:partner learning (Score 4, Informative)

There is precious little research to date comparing the efficiency of two skilled and experienced programmers doing full-time pair programming with what they produce working alone except when they feel the need to collaborate in real time, and what there is isn't nearly as favourable.

One interesting data point is the study Evaluating Pair Programming with Respect to System Complexity and Programmer Expertise by Erik Arisholm et al. from Simula Research Laboratory, published in the February 2007 issue of Transactions on Software Engineering. There's a good summary on the Catenary blog.

This study is more realistic in that the research subjects were professional Java consultants, rather than college students. However, it appears the study did not allow the subjects to collaborate with anyone outside the pair (or at all, for the solo subjects).

The abstract of the study:
A total of 295 junior, intermediate, and senior professional Java consultants (99 individuals and 98 pairs) from 29 international consultancy companies in Norway, Sweden, and the UK were hired for one day to participate in a controlled experiment on pair programming. The subjects used professional Java tools to perform several change tasks on two alternative Java systems with different degrees of complexity. The results of this experiment do not support the hypotheses that pair programming in general reduces the time required to solve the tasks correctly or increases the proportion of correct solutions. On the other hand, there is a significant 84 percent increase in effort to perform the tasks correctly. However, on the more complex system, the pair programmers had a 48 percent increase in the proportion of correct solutions but no significant differences in the time taken to solve the tasks correctly. For the simpler system, there was a 20 percent decrease in time taken but no significant differences in correctness. However, the moderating effect of system complexity depends on the programmer expertise of the subjects. The observed benefits of pair programming in terms of correctness on the complex system apply mainly to juniors, whereas the reductions in duration to perform the tasks correctly on the simple system apply mainly to intermediates and seniors. It is possible that the benefits of pair programming will exceed the results obtained in this experiment for larger, more complex tasks and if the pair programmers have a chance to work together over a longer period of time.