The majority of research work carried out in the software cost estimation field has been devoted to algorithmic models. However, by an overwhelming majority, expert judgement is the most commonly used estimation method. A Dutch study carried out by [HEMSTRA] revealed that 62% of estimators / organisations use this intuition technique and a study carried out by [VIGDER & KARK] also confirmed the techniques popularity. In its crudest form the expert judgement method involves consultation with one or more local experts who are knowledgeable about the development environment or application domain to estimate the effort required to complete a software project.
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.
Despite widespread use, the method seems to have received a rather poor reputation and is often regarded as subjective and unstructured making it vulnerable against more structured methods. A more structured form a expert judgement is the Wideband Delphi Approach.
An excellent paper by [HUGHES 96] discusses expert judgement in detail identifying its strengths and weaknesses , but redressing the balance that expert judgement is simply a ‘guess’ and identifying how useful the method can be in industry.
Assessment of Expert Judgement
