Early work on this question observed releases and tried to lay down the
so-called laws of software evolution. Other approaches used sophisticated
statistical analysis to model software decay and to predict the risk of
changes. More recent approaches turned towards developers and supported
them with powerful recommender systems.
However, the data in version control systems is limited and thus many
approaches include program analysis and bug databases. Using such data,
your version control system can tell you that programmers make more bugs on
Thursdays.