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Making Software by Greg Wilson, Andy Oram

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Team Productivity Variation in Software Development

Software experts have long observed that team productivity varies about as much as individual productivity does—by an order of magnitude [Mills 1983]. Part of the reason is that good programmers tend to cluster in some organizations and bad programmers in others, an observation that has been confirmed by a study of 166 professional programmers from 18 organizations [Demarco and Lister 1999].

In one study of seven identical projects, expended effort varied by a factor of 3.4 to 1 and program sizes by a factor of 3 to 1 [Boehm et al. 1984]. In spite of the productivity range, the programmers in this study were not a diverse group. They were all professional programmers with several years of experience who were enrolled in a computer-science graduate program. It’s reasonable to assume that a study of a less homogeneous group would turn up even greater differences. An earlier study of programming teams observed a 5-to-1 difference in program size and a 2.6-to-1 variation in the time required for a team to complete the same project [Weinberg and Schulman 1974].

After reviewing more than 20 years of data in constructing the COCOMO II estimation model, Barry Boehm and other researchers concluded that developing a program with a team in the 15th percentile of programmers ranked by ability typically requires about 3.5 times as many staff-months as developing a program with a team in the 90th percentile [Boehm et al. 2000]. The difference ...

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