Reference #139: Peopleware
Performance variation is stronger across companies than within them.
The best performers tend to cluster in some organisations while the worst performance cluster in others. This suggests a large role of environment and company culture on performance.
As Mills wrote in 1988, "while a ten-to-one productivity differential among programmers is understandable, there is also a ten-to-one difference in productivity among software organisations."
DeMarco, Lister. Peopleware, 2013. (46-47)