Effort Estimation with Story Points and COSMIC Function Points

An Industry Case Study

Commeyne, C., Abran, A., Djouab, R.

In Agile software projects developed using the Scrum process, Story Points are often used to estimate project effort. Story Points allow comparison of estimated effort with actual effort, but do not provide a size of the software developed and, therefore, do not allow determination of the productivity achieved on a project nor comparison of performance across projects and across organizations. In contrast to Story Points, international standards on functional size measurement, such as ISO 19761 (COSMIC Function Points), provide explicit measurement of software size for both estimation and benchmarking purposes. This study reports on the performance of estimation models built using Story Points and COSMIC Function Points and shows that, for the organization in which the data was collected, the use of COSMIC Function Points leads to estimation models with much smaller variances. The study also demonstrates that the use of COSMIC Function Points allows objective comparison of productivity across tasks within a Scrum environment.

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