Introduction to Wide Band Delphi
Wide Band Delphi (WBD) estimation approach is a technique that was developed in the 1940s at Rand Corporation. This approach involves a team of experts preparing individual estimates for a project, similar to the consensus-based approach for estimation. The WBD estimation approach is a more advanced version of the Delphi method, where the estimation team uses statistical methods to refine and improve the estimates.
The WBD estimation approach starts with the same steps as the consensus-based approach, where the project manager selects a team and a moderator, and the team consists of 3-7 team members with representation from all groups, such as development, testing, etc. The moderator should be familiar with the Delphi process, and it is ideal to have the project manager as part of the estimation team. However, the project manager should not be the moderator as he will have a stake in the outcome of the estimation.
Steps Involved in Wide Band Delphi Estimation
The first step is the planning phase, where the kickoff meeting takes place. During the kickoff meeting, the team explains the Delphi process, reviews the vision and scope document or any supporting documents as prerequisites, and discusses the goals of the estimation session. The team then brainstorm and notes down the assumptions, generates the initial work breakdown structure (WBS), and decides upon the unit for estimation.
The next step is individual estimation, where each estimator estimates the time required for each task, adds any additional tasks to the WBS, and includes any missing assumptions. The difference in the WBD approach is that each estimator also provides a range of estimates for each task, including an optimistic estimate, a pessimistic estimate, and a most likely estimate.
The third step is the estimation meeting, where the moderator shares the estimates so that estimators can see the range of estimates. The individual estimates are not shared, and the team members revise estimates based on group discussions. The estimates are revised until no estimator wants to change his/her estimates, and the estimators agree that the estimates are acceptable.
In the WBD approach, the moderator also uses statistical methods to refine and improve the estimates. The moderator calculates the average of the most likely estimates and determines the standard deviation of the estimates. The standard deviation is used to calculate the optimistic and pessimistic estimates. The moderator then asks the estimators to provide additional estimates based on the optimistic and pessimistic estimates.
Example of Wide Band Delphi Estimation Technique
An example of the WBD estimation approach is when there are three estimators, A, B, and C, who are told to prepare the time required to prepare test scenarios for a project. The initial estimations provided were A – 18 Hours, B – 38 Hours, and C – 58 Hours. The moderator then calculates the average estimate as 38 hours and returns this with their original estimates to the estimators.
Figure: Iterations and Estimated Effort
The estimators then meet and discuss the estimates, and the initial estimations provided were A – 31 Hours, B – 32 Hours, and C – 33 Hours. The moderator then calculates the average estimate as 32 hours and asks the estimators if they agree with this as the estimate. The moderator also calculates the optimistic and pessimistic estimates based on the standard deviation of the estimates.
The final step is to assemble tasks and review results, where the project manager works with the team and collects the estimates from team members, compiles the final WBS, estimations, and assumptions, and reviews the final estimates with the estimation team. You can find additional details of the technique by reading this e-book From Guesswork to Accuracy: Mastering Software Test Estimation
The Wide Band Delphi (WBD) estimation approach is an advanced version of the Delphi method, where the estimation team uses statistical methods to refine and improve the estimates. This technique is ideal for projects that require a more accurate and precise estimate. The WBD approach is similar to the consensus-based approach for estimation, where the team of experts prepares individual estimates, builds a complete task.
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