Models for the evolution of OS projects

Software evolution and maintenance is largely based on data gathered through years of experience: understanding and improving software is often a matter of how much data is available. Open Source software offers the opportunity to analyze closely all the phases in the evolution of a project. What's more, data regarding its evolution is generally available for inspections. Based on simply code analyses, lots of questions about its efficiencies can't be resolved. It would be necessary to study the process from the inside, understanding who or what drove what improvement and so on. Still a quantitative analysis gives several insights about how much code is created and evolved by developers. This study takes a sample of 12 open source projects and gives some statistics to analyze their evolution. The purpose is here to compare what is commonly know in software evolution in traditional environments, and what happens instead in open environments.