One of the most replicated results in software engineering research is the 10-fold difference in productivity and quality between different programmers with the same levels of experience. Researchers have also found that this difference applies at the team level, even to different teams working within the same industries.
The original study that found huge variations in individual programming productivity was conducted in the late 1960s by Sackman, Erikson, and Grant [Sackman et al. 1968]. They studied professional programmers with an average of 7 years’ experience and found that the ratio of initial coding time between the best and worst programmers was about 20 to 1; the ratio of debugging times over 25 to 1; of program size 5 to 1; and of program execution speed about 10 to 1. They found no relationship between a programmer’s amount of experience and code quality or productivity.
Detailed examination of Sackman, Erickson, and Grant’s findings shows some flaws in their methodology (including combining results from programmers working in low-level programming languages with those working in high-level programming languages). However, even after accounting for the flaws, their data still shows more than a 10-fold difference between the best programmers and the worst.
In the years since the original study, the general finding that “There ...