My COCOMO: Building Your Own Incremental Software Build Estimation Tools

This paper describes work performed in Rolls-Royce to develop an Incremental Software Build Cost and Schedule estimation tool. The software builds incorporated in the analysis were performed over a period of 10 years with a reasonably consistent team of engineers and software development environment - hence many of the environmental factors developed in software estimation tools like COCOMO (1) were effectively held constant in this study. This allowed the correlation to concentrate on measuring the effects of team size and process change on cost and schedule estimates. These correlations have been integrated with the COCOMO model to create a system that can account for team size for both cost and schedule estimation – “My COCOMO”. The first part of the paper describes factors that can influence the measurement of “effort” and how these may add noise to correlations. The second part of the paper describes how team size can be incorporated into the estimation model to reduce scatter in predictions, and concludes by showing how the resulting correlations can be incorporated into an incremental software build estimation tool which accounts for the level of cost and schedule risk the project is prepared to take when developing a software build. The third part describes the effect of a process change that was introduced and the statistical verification of the significance of the process change on the effort required for software builds.