It is known that well over 50% of replacement projects fail. Requirements gathering go someway to contributing to this statistic; if the requirements we gather for the new system do not match those of the system to be replaced then the project is bound to fail, at least in part.

This paper proposes an empirical metric that assists measuring the confidence in the requirements extracted from a legacy system. This metric capitalises on five techniques for gathering requirements from legacy systems and caters for a number of different types of project. The metric can be used to estimate the likelihood of a project?s success or failure and is evaluated by two industrial case studies; conclusions are drawn from these and directions for further work are presented.