A general method for estimating various numerical values. The values are pulled out of a hat (Stetson), i.e. made up. The purpose of Harrison is to increase credibility.
As a generalization, things other than numbers can also be estimated using the Stetson-Harrison method.
Our group did not have any experience or competence in determining a suitable scope for the project, so an estimate for the scope was produced using the Stetson-Harrison method.