The method relies heavily on the experience of their knowledge in similar development environments and historically maintained databases on completed projects and the accuracy of theses past projects. However, the study carried out by [VIGDER & KARK] indicated that in general estimators did not refer to previous projects as it was too difficult to access or the expert could not see how the information would help in the accuracy of the estimate. The study claimed that the majority of estimators tended to use their memories of previous projects. If more than one expert is used the weighted average of their estimates are taken. There are obvious risks with this method. As the project may have some unique features which could take longer than anticipated. The weighted average is also very much dependent on the competence of the estimator. However, a particular strength of using an expert is that they can raise unique strengths and weaknesses of the local organisational characteristics.
