Predicting maintenance effort with function points

Function point analysis (FPA) is a well-known method to measure the functionality of a system, from the user's point of view. Both Albrecht's (1979) original model and a local variant we studied assume that effort is primarily related to the size of a change. Analysis of data gathered on a major system over a period of 18 months does not confirm this relation. Rather our data suggests that the size of the component to be changed has a much larger impact on effort than the size of the change itself. Furthermore, the various corrective factors of the function point model do not help to improve effort estimates in the environment we studied. Finally, we found that expert estimates outperform the function point estimates, while analogy-based estimates slightly outperform the expert estimates