Is duplicate code more frequently modified than non-duplicate code in software evolution?

Various kinds of research efforts have been performed on the basis that the presence of duplicate code has a negative impact on software evolution. A typical example is that, if we modify a code fragment that has been duplicated to other code fragments, it is necessary to consider whether the other code fragments have to be modified simultaneously or not. In this research, in order to investigate how much the presence of duplicate code is related to software evolution, we defined a new indicator, modification frequency. The indicator is a quantitative measure, and it allows us to objectively compare the maintainability of duplicate code and non-duplicate code. We conducted an experiment on 15 open source software systems, and the result showed that the presence of duplicate code does not have a negative impact on software evolution.