Often organisations employ third party contractors to carry out modifications and upgrades to an existing software product. This is usually done because of a lack of resource within the organisation: the software support staff could be busy on other projects, they could have a lack of expertise in the area of the work, or the job could just be too big to be done internally. Whatever the reason, bringing in an external contractor can have huge implications on the evolution of the software.

As part of an evolution case study of a software product in use by the UK Royal Air Force (RAF), where third party contractor modifications were done on a regular basis, the implications of this third party work is being examined. The quality of the delivered software from both the in-house team and the contractor has been measured with particular attention to the software complexity.

Preliminary results show that the software product experienced an increase of complexity throughout its evolution, specifically in the areas delivered by the contractors.