Investigating the Significance of the Bellwether Effect to Improve Software Effort Prediction: Further Empirical Study

TL;DR

This study empirically confirms the existence of Bellwether projects in software effort prediction and demonstrates that using a moving window of recent exemplary projects improves prediction accuracy.

Contribution

It provides empirical evidence that Bellwethers exist and are effective when selected with specific size and age parameters for software effort prediction.

Findings

Bellwethers are present in SEP data.

A moving window of 50-80 recent projects enhances prediction accuracy.

Bellwethers should be no more than 2 years old.

Abstract

Context: In addressing how best to estimate how much effort is required to develop software, a recent study found that using exemplary and recently completed projects [forming Bellwether moving windows (BMW)] in software effort prediction (SEP) models leads to relatively improved accuracy. More studies need to be conducted to determine whether the BMW yields improved accuracy in general, since different sizing and aging parameters of the BMW are known to affect accuracy. Objective: To investigate the existence of exemplary projects (Bellwethers) with defined window size and age parameters, and whether their use in SEP improves prediction accuracy. Method: We empirically investigate the moving window assumption based on the theory that the prediction outcome of a future event depends on the outcomes of prior events. Sampling of Bellwethers was undertaken using three introduced Bellwether methods (SSPM, SysSam, and RandSam). The ergodic Markov chain was used to determine the stationarity of the Bell-wethers. Results: Empirical results show that 1) Bellwethers exist in SEP and 2) the BMW has an approximate size of 50 to 80 exemplary projects that should not be more than 2 years old relative to the new projects to be estimated. Conclusion: The study's results add further weight to the recommended use of Bellwethers for improved prediction accuracy in SEP.