Estimation

Chapter 3

Applied Software Project Management, Stellman & Greene

Decomposing a project into tasks

By feature By project phase Some combination

The most accurate estimates... Rely on prior experience

Teams review previous project results Find how long previous projects took

Estimates will change because: People leave the project/get sick Technical problems arise Needs of the organization change

The unexpected will almost certainly happen

Two people may disagree on how long a task will take...

Generally because of assumptions on what is required

A good project manager can reduce the uncertainty by creating the vision and scope document

Assumptions

Help when dealing with incomplete information

Should be written down and discussed Brainstormed by team to identify as

many assumptions as possible

Questions to help identify assumptions Are there project goals that are known to the team, but are

not written down? Are there any concepts, terms, or definitions that need to be

clarified? Are there standards that must be me, but will be expensive

to comply with? How will the development of this project differ from that of

previous projects? Will there be new tasks added that were not previously performed?

Are there technology and architecture decisions that have already been made?

What changes are likely to occur elsewhere in the organization that could cause this estimate to be inaccurate?

Are there issues that the team is known to disagree on that will affect the project?

Distrust can undermine estimates

Politics “Rule” of cutting by third, half... Lack of trust may cause engineers to

inflate their estimates

Wideband Delphi Estimation

Developed in 1940s by Rand Corp. for forecasting

This process produces: Set of estimates for the schedule WBS List of assumptions (for Vision &Scope) Discussion and time to correct each other

Depends on Vision and Scope document

Delphi Process led by moderator Kickoff meeting

Create WBS and list of assumptions After the meeting each member creates an

effort estimate for each task

Estimation session Team revises estimates as a group and reaches

consensus

Then project manager summarizes results and reviews with team

See Table 3-1

Details...

Each team member must make an effort to estimate each task honestly

Free flow of information is essential Sessions can get heated Include observers to sit in on the

meetings: stakeholders, users, managers

Role of the moderator

Should ideally not have a stake in the project Listens to discussion Asks open-ended questions Challenges team to address the issues Ensures that everyone is contributing

Kickoff meeting Meeting activities

Moderator explains the process All read the Vision and Scope if they have not Moderator goes over the goal statement

prepared by the PM and the moderator Team discusses the product and brainstorms

assumptions Team generates a task list of ~10-20 major

tasks => top level of WBS Team agrees on units of estimation (days,

weeks, pages, etc.) WBS is generated

Individual preparation Each team member generates a set of

preparation results as shown in Figure 3-1 Task list with units of effort Calendar waiting time Project overhead tasks

Estimation session Members bring their individual work and ...

1. Fill out estimation forms as in Figure 3-2: one row for each task and totaled

2. Moderator collects and plots totals on a line: Figure 3-3

3. Each estimator gives clarification and changes to the task list

4. Team resolves issues or disagreements5. Estimators revise their estimates by filling in the

next Delta column Cycle repeats until agreement or two hours

Assembling tasks and Reviewing results

Figure 3-5 shows each estimator’s final estimates

Best and worst cases are shown Assumptions are put in final form and

now entered into Vision and Scope What happens when one team

member continues to disagree?

Other Techniques PROBE COCOMO II The Planning Game

For Next Time: Vision and Scope Readings