Refactoring is the practice of changing source code without altering its external behavior. It is widely used since it is acknowledged to have a positive effect on software quality. However, different studies on the impact of Refactoring on software quality led to contrasting results. This might be due also to the fact that research works on Refactoring rely on different approaches to collect information about the refactoring activity on software repositories. Having a reliable approach is fundamental to draw solid conclusions. In this paper we empirically analyzed two of the most popular approaches to detect the refactoring activity on software repositories, finding that they return different outcomes. These results should be taken into account by researchers while designing the experimental settings of their studies.