A Ranking Stability Indicator for Selecting the Best Effort Estimator in Software Cost Estimation

Software effort estimation research shows that there is no universal agreement on the “best” effort estimation approach. This is largely due to the “ranking instability” problem, which is highly contingent on the evaluation criteria and the subset of the data used in the investigation. There are a large number of different method combination exists for software effort estimation, selecting the most suitable combination becomes the subject of research in this paper. Unless we can reasonably determine stable rankings of different estimators, we cannot determine the most suitable estimator for effort estimation. This paper reports an empirical study using 90 estimation methods applied to 20 datasets as an attempt to address this question. Performance was assessed using MAR, MMRE, MMER, MBRE, MIBRE, MdMRE, PRED(25) and compared using a Wilcoxon ranked test (95%). An comprehensive empirical experiment was carried out. Result shows prior studies of ranking instability of effort estimation approaches may have been overly pessimistic. Given the large number of datasets, it is now possible to draw stable conclusions about the relative performance of different effort estimation methods and to select the most suitable ones for the study under investigation. In this study, regression trees or analogy-based methods are the best performers in the experiment, and we recommend against neural nets or simple linear regression. Based on the proposed evaluation method, we are able to determine the most suitable local estimator for software cost estimation, an important process in the application of any effort estimation analysis.