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Empirical Software Engineering

As researchers investigate how software gets made, a new empire for empirical research opens up

Greg Wilson, Jorge Aranda

Two-Headed Approach

2011-11WilsonF3.jpgClick to Enlarge ImageMetrics research looks at the code that programmers produce, but at least as much research effort has focused on how they produce it. An interesting case is pair programming, a work style that burst onto the scene in the late 1990s (though people have been using it informally for as long as programming has existed). In pair programming, two programmers sit at a single workstation and create code together. The driver handles the keyboard and mouse, while the navigator watches, comments and offers corrections. Many programmers have noticed over the years that duos like this seem to produce code more quickly and with fewer bugs. If asked, they would probably say that the benefits arise because different people naturally notice different sorts of things, or because not having to type gives the navigator more time to think, or possibly that having an audience makes the driver think more carefully. But is pair programming actually better, and if so, which of the possible explanations is the reason?

The first empirical study of pair programming, by Temple University professor John Nosek in 1998, studied 15 programmers, 5 working alone (the control group), the other 10 in 5 pairs. A challenging programming problem was given, with a time limit of 45 minutes. The results were statistically significant. Solutions produced by the pairs took 60 percent more total time, but dividing the total time by two, they completed the tasks 20 percent faster. And the author of the study reported that the pairs produced higher-quality code.

Subsequent studies with larger groups over longer periods of time, summarized by Laurie Williams at North Carolina State University, have expanded on these early results. Pair programmers tend to produce code that is easier to understand, and they do so with higher morale. Their productivity may fall initially as the programmers adjust to the new work style, but productivity recovers and often surpasses its initial level as programmer teams acquire experience. Related studies have also given insight into what actually happens during pair programming. For example, successful pairs often don’t work together for a full day—pairing can be mentally exhausting. Changing partners regularly seems to help, and swapping roles periodically between driver and navigator helps keep programmers engaged.

These results can even influence hardware design. Some teams have two people who both do best when they have control of the keyboard. Why not provide dual keyboards and mice? Jan Chong and Tom Hurlbutt tested this approach at Stanford University in 2007 and found it a worthwhile advance in pair programming, a finding subsequently supported by additional studies by Andreas Höfer at the University of Karlsruhe and by Sallyann Freudenberg, a software coach. Once again, what we’re seeing is the science rapidly improving as early studies generate questions and methods for follow-on research.

What we also see is that being right isn’t always enough to effect change. Despite the accumulation of evidence in its favor, pair programming is still very much the exception in industry. Managers and programmers alike often brush the data away, clinging to the idea that putting two people on one job must double staffing requirements and therefore cannot deliver efficiency. This is an unfortunate phenomenon in many fields. Some people resist change tenaciously, even in the face of evidence and at the risk of failure.

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