Empirical Techniques in software estimation for software project management is based on making an executed guess of project parameters. Here experience in the development of a similar product is helpful. There are the following types of estimation techniques:-
Expert Judgement
It is the most widely used empirical software estimation technique. In this approach, an expert makes an executed guess of problem size and hence the effort required after analyzing the problem thoroughly.
Here the experts estimate the cost of different components and then combines them to arrive at an overall estimate. However, this technique is subject to human errors and individual bias. Also, an expert in estimating may not have complete experience and knowledge in all the aspects of the project. This can be refined by making a group of experts perform the required task. This minimizes factors like individual overside, lack of familiarity with a particular aspect of a project. Also, personal bias and the desire to win a contract make overly optimistic estimates can also be minimized. However, estimation by a group of experts may still exhibit bias due to political considerations.
Estimation By Analogy
This is also called case-based reasoning. Here the estimation identifies previously completed projects (source cases) with similar characteristics. To the new project (target case). The estimator them identifies difference between the source and the target and adjusts the base estimate to produce a final estimate of the new project.
This technique is mainly used when you have sufficient information of previous project. Here an addition problem or task is to identify the similarities and differences between the applications with large number of pasts project.
Delphi Cost Estimation
The Delphi cost estimation approach overcomes come of the shortcomings of the expert judgement approach. Delphi estimation is carried out by a group of experts and a coordinator. Who provides each estimator with a copy of the software requirement specification(SRS) and a form for recording the cost estimate.
The estimators after giving their individual estimate submit it to the coordinator who then prepares and distributes the summary of the responses of all the estimators. In this process, any unusual rationale is also noted by the coordinator based on this summary the estimators re-estimate and the process iterates for several rounds. After which the co-ordinator finally compiles the result of the final estimate.