Empirical estimation technique:
Empirical estimation technique are based on the data taken from the previous project and some based on guesses and assumptions.
There are many empirical estimation technique but most popular are
Expert Judgement Technique
Delphi Cost Technique
Expert judgement technique:An expert makes an educated guess of the problem size after analyzing the problem thoroughly. Expert estimate the cost of different components that is modules and sub modules of the system.
Human error, considering not all factors and aspects of the project, individual bias, more chances of failure.
Estimation by group of experts minimises factors such as individual oversight, lack of familiarity with a particular aspect of a project, personal bias and desired to win a contract through overly optimistic estimates.
Delphi cost estimation:
Role of Members: Coordinator provide a copy of Software Requirement Specification(SRS) document and a form of recording it cost estimate to each estimator.
Estimator: It complete their individual estimate anomalously and submit to the coordinator with mentioning, if any, unusual characteristics of product which has influenced his estimation.
The coordinator and distribute the summary of the response to all estimator and they re-estimate them.
This process is Iterated for several rounds.
No discussion is allowed among the estimator during the entire estimation process because there may be many estimators get easily influenced by rationale of an estimator who may be more experienced or senior.
After the completion of several iterations of estimation, the coordinator takes the responsibility of compiling the result and preparing the final estimates.