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Wideband Delphi estimation process Print E-mail
To someone who has never estimated a project in a structured way, estimation seems little more than attempting to predict the future. This view is reinforced when off-the-cuff estimates are inaccurate and projects come in late. But a good formal estimation process, one that allows the project team to reach a consensus on the estimates, can improve the accuracy of those estimates, making it much more likely that projects will come in on time. Wideband Delphi is an estimation process process that is straightforward to implement. Using it, a project manager can help the team to create successful estimates for any software project by using sound techniques and understanding what makes estimates more accurate.

The Delphi Process

The Wideband Delphi estimation method was developed in the 1940s at the Rand Corporation as a forecasting tool. It has since been adapted across many industries to estimate many kinds of tasks, ranging from statistical data collection results to sales and marketing forecasts. It has proven to be a very effective estimation tool, and it lends itself well to software projects. The repeatable process for Wideband Delphi presented here was developed in the 1990s by Mary Sakry and Neil Potter of The Process Group.

To use Wideband Delphi, the project manager selects a moderator and an estimation team with three to seven members. The Delphi process consists of two meetings run by the moderator. The first meeting is the kickoff meeting, during which the estimation team creates a WBS and discusses assumptions. After the meeting, each team member creates an effort estimate for each task. The second meeting is the estimation session, in which the team revises the estimates as a group and achieves consensus. After the estimation session, the project manager summarizes the results and reviews them with the team, at which point they are ready to be used as the basis for planning the software project.

Name  Wideband Delphi script
Purpose A project team generates estimates and a work breakdown structure.
A repeatable process for estimation. Using it, a project team can generate a consensus on estimates for the completion of the project.
Work Products
Vision and scope document, or other documentation that defines the scope of the work product being estimated
Work breakdown structure (WBS)
Effort estimates for each of the tasks in the WBS
Entry Criteria
The following criteria should be met in order for the Delphi process to be effective:
  • The vision and scope document (or other documentation that defines the scope of the work product being estimated) has been agreed to by the stakeholders, users, managers and engineering team. If no vision and scope document is available, there must be enough supporting documentation for the team to understand the work product.
  • The kickoff meeting and estimation session have been scheduled, with at least two hours allowed for each.
  • The project manager and the moderator agree on the goal of the estimation session by identifying the scope of the work to be estimated.
 Basic Course of Events
  1. Choose the team. The project manager selects the estimation team and a moderator. The team should consist of 3 to 7 project team members. The team should include representatives from every engineering group that will be involved in the development of the work product being estimated.
  2. Kickoff meeting. The moderator prepares the team and leads a discussion to brainstorm assumptions, generate a WBS and decide on the units of estimation.
  3. Individual preparation. After the kickoff meeting, each team member individually generates the initial estimates for each task in the WBS, documenting any changes to the WBS and missing assumptions.
  4. Estimation session. The moderator leads the team through a series of iterative steps to gain consensus on the estimates. At the start of the iteration, the moderator charts the estimates on the whiteboard so the estimators can see the range of estimates. The team resolves issues and revises estimates without revealing specific numbers. The cycle repeats until either no estimator wants to change his or her estimate, the estimators agree that the range is acceptable or two hours have elapsed.
  5. Assemble tasks. The project manager works with the team to collect the estimates from the team members at the end of the meeting and compiles the final task list, estimates and assumptions.
  6. Review results. The project manager reviews the final task list with the estimation team.
  1. During step 1, if the team determines that there is not enough information known about the project to perform an estimate, the script ends. Before the script can be started again, the project manager must document the missing information by creating or modifying the vision and scope document (see Chapter 2).
  2. During either step 1 or 3, if the team determines that there are outstanding issues that must be resolved before the estimate can be made, they agree upon a plan to resolve the issues and the script ends.
 Exit Criteria
 The script ends after the team has either generated a set of estimates or has agreed upon a plan to resolve the outstanding issues.

Kickoff Meeting

The moderator leads the meeting, which consists of the following activities:
  • The moderator explains the Wideband Delphi method to any new estimators.
  • If any team member has not yet read the vision and scope document and supporting documentation, the moderator reviews it with the team. (If this happens, the meeting should be expected to take an extra half-hour to hour.)
  • The moderator reviews the goal of the estimation session with the team, and checks that each team member is sufficiently knowledgeable to contribute.
  • The team discusses the product being developed and brainstorms any assumptions.
  • The team generates a task list consisting of 10-20 major tasks. These tasks represent the top level of the work breakdown structure—additional detail can be generated later and/or discussed in the assumptions. This high-level task lists is the basis for the estimates that are going to be created.
  • The team agrees on the units of estimation (days, weeks, pages, classes, etc.).

Individual Preparation

After the kickoff meeting, the moderator writes down all of the assumptions and tasks that were generated by the team during the kickoff meeting and distributes them to the estimation team. Each team member independently generates a set of preparation results, a document which contains an estimate for each of the tasks, any assumptions that the team member made in order to create the estimates and any additional tasks which should be included in the WBS but which the team missed during the kickoff meeting. (The figure below shows the format of the individual preparation results.) Each team member builds preparation results by first filling in the tasks, and then estimating the effort for each task. An estimate for each task should be added to the “Tasks to achieve goal” section of the preparation results; the “Time” column should contain the estimate for each task.
Individual Preparation Results
Individual Preparation Results
Individual Preparation Results

Estimation session

The estimation session starts with each estimator filling out an estimation form. Blank estimation forms should be handed out to meeting participants, who fill in the tasks and their initial estimates from their individual preparations. During the estimation session, the team members will use these estimation forms to modify their estimates. After the estimation session, they will serve as a record of each team member’s estimates for the individual tasks, which the project manager uses when compiling the results.
Filled-in Estimation Form
Filled-in estimation form
(© The Process Group, copied with permission)
The moderator then leads the team through the estimation session:
1.    The moderator collects all of the estimate forms. The estimates are tabulated on a whiteboard by plotting the totals on a line (see Figure 3-3). The forms are returned to the estimators.
Initial Estimates
Initial estimates
2.    Each estimator reads out clarifications and changes to the task list written on the estimation form. Any new or changed tasks, discovered assumptions or questions are raised. Specific estimate times are not discussed.
3.    The team resolves any issues or disagreements that are brought up. Since individual estimate times are not discussed, these disagreements are usually about the tasks themselves, and are often resolved by adding assumptions. When an issue is resolved, team members should write clarifications and changes to the task list on their estimation forms. This usually takes about 40 minutes for the first round, and 20 minutes for the following rounds.
4.    The estimators all revise their individual estimates by filling in the next “Delta” column on their forms. (Using a delta allows the estimators to write “+4” or “-3” to add 4 or remove 3 from the estimate. They write the new total at the bottom of the sheet.)
This cycle repeats until either all estimators agree that the range is acceptable, the estimators feel they do not need to change their estimates, or two hours have elapsed.
Converging Estimate Results
Converging estimate results

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