Comparing Effort Estimates Based on Use Case Points with Expert Estimates

Use case models are used in object-oriented analysis for capturing and describing the functional requirements of a system. Attributes of a use case model may therefore serve as measures of the size and complexity of the functionality of a system. Many organizations use a system's use case model in the estimation process. This paper reports the results from a study conducted to evaluate a method for estimating software development effort based on use cases, the use case points method, by comparing it with expert1 estimates. A system was described by a brief problem statement and a detailed use case model. The use case points method gave an estimate that was closer to the actual effort spent on implementing the system than most estimates made by 37 experienced professional software developers divided into 11 groups (MRE of 0.21 versus MMRE of 0.37). The results support existing claims that the use case points method may be used successfully in estimating software development effort. They also show that the combination of expert estimates and method based estimates may be particularly beneficial when the estimators lack specific experience with the application domain and the technology to be used.