From Story Points to COSMIC Function Points in Agile Software Development

A Six Sigma perspective

Fehlmann, Th., Santillo, L.

The spreading of agile methodologies in software development raises the question
of how to measure requirements once more, as it happened in ‘traditional’ software
industry development approaches decades ago. The difference is that requirements
are not known in advance but detected as User Stories while iterating and enhancing
the software product from one agile ‘Sprint’ to the other.
Some authors – promoting best practices for agile software development – propose
Story Points to size User Stories (e.g., Scrum, with Story Cards), yet not combined
with base project estimation. Story Points are not standardized, thus leading to
eventual misconceptions and quantitative differences among practitioners and
domains. The uncertainty implied in such approach can therefore propagate to any
estimate based on it, not to mention the difficulty in accurately tracing requirements
and their variation over the project and across project iterations.
This work investigates benefits from adopting a standardized Functional Size
Measurement (FSM) method, such as COSMIC Function Points, in place of Story
Points. Using a Transfer Function (from the Six Sigma practice) that transforms
size into effort spent within a particular agile team, defect density prediction can
be made using sensitivity analysis.