Comparative Evaluation of Functional Size Measurement Methods: An Experimental Analysis

A number of Functional Size Measurement (FSM) methods have been proposed in the literature, but so far there has been no systematic evaluation of these methods. A major criticism is that little attention has been paid to the empirical validation of FSM methods. By empirical validation we refer to the evaluation of the efficacy of the method and its likely adoption in practice using experimental techniques and statistical data analysis. This paper describes a laboratory experiment which compares Function Points Analysis, a standard FSM method supported by the International Functional Point Users Group (IFPUG FPA) and OOMethod Function Points (OOmFP), a recently proposed FSM method for sizing object-oriented (OO) software systems that are developed using the OO-Method approach. The goal is to investigate whether OOmFP results in better size assessments and is more likely to be adopted in practice, within the context of an OO-Method development process. As OOmFP and IFPUG FPA are FSM methods, only the functional size of a software system is quantified, meaning that only the functional system requirements as seen from the user’s perspective are considered as contributing to system size. The methods are compared using a range of performance-based and perception-based variables, including efficiency (effort required to apply the methods), reproducibility, accuracy, perceived ease of use, perceived usefulness and intention to use. An important contribution is the development and empirical testing of a theoretical model for evaluating FSM methods in general. The results show that OOmFP is more timeconsuming that IFPUG FPA but the measurement results are more consistent and accurate. Also, OOmFP is perceived to be a useful FSM method in the context of OO-Method systems development. Moreover, the theoretical model proposed might help to bridge the gap between research and practice in Empirical Software Engineering research, as it addresses the issue of method adoption in practice, which has been ignored by ESE researchers.