The Cost And Schedule Estimating Process

Project plans need to be derived from two perspectives. The first is a forward-looking, top-down approach. It starts with an understanding of the general requirements and constraints, derives a macro-level budget and schedule, then decomposes these elements into lower level budgets and intermediate milestones. From this perspective, the following planning sequence would occur:

1. The software project manager (and others) develops a characterization of the overall size, process, environment, people, and quality required for the project.

2. A macro-level estimate of the total effort and schedule is developed using a software cost estimation model.

3. The software project manager partitions the estimate for the effort into a top-level WBS using guidelines such as those in Table 10-1. The project manager also partitions the schedule into major milestone dates and partitions the effort into a staffing profile using guidelines such as those in Table 10-2. Now there is a project-level plan. These sorts of estimates tend to ignore many detailed project-specific parameters.

4. At this point, subproject managers are given the responsibility for decomposing each of the WBS elements into lower levels using their top-level allocation, staffing profile, and major milestone dates as constraints.

The second perspective is a backward-looking, bottom-up approach. You start with the end in mind, analyze the micro-level budgets and schedules, then sum all these elements into the higher level budgets and intermediate milestones. This approach tends to define and populate the WBS from the lowest levels upward. From this perspective, the following planning sequence would occur:

1. The lowest level WBS elements are elaborated into detailed tasks, for which budgets and schedules are estimated by the responsible WBS element manager. These estimates tend to incorporate the project-specific parameters in an exaggerated way.

2. Estimates are combined and integrated into higher level budgets and milestones. The biases of individual estimators need to be homogenized so that there is a consistent basis of negotiation.

3. Comparisons are made with the top-down budgets and schedule milestones. Gross differences are assessed and adjustments are made in order to converge on agreement between the top-down and the bottom-up estimates.

Milestone scheduling or budget allocation through top-down estimating tends to exaggerate the project management biases and usually results in an overly optimistic plan. Bottom-up estimates usually exaggerate the performer biases and result in an overly pessimistic plan. Iteration is necessary, using the results of one approach to validate and refine the results of the other approach, thereby evolving the plan through multiple versions. This process instills ownership of the plan in all levels of management.

These two planning approaches should be used together, in balance, throughout the life cycle of the project. During the engineering stage, the top-down perspective will dominate because there is usually not enough depth of understanding nor stability in the detailed task sequences to perform credible bottom-up planning. During the production stage, there should be enough precedent experience and planning fidelity that the bottom-up planning perspective will dominate. By then, the top-down approach should be well tuned to the project-specific parameters, so it should be used more as a global assessment technique. Figure 10-4 illustrates this life-cycle planning balance.

Project Management Made Easy

Project Management Made Easy

What you need to know about… Project Management Made Easy! Project management consists of more than just a large building project and can encompass small projects as well. No matter what the size of your project, you need to have some sort of project management. How you manage your project has everything to do with its outcome.

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  • oscar
    Why size and cost are estimated in software project planning?
    12 months ago
  • julia gruenewald
    What is cost and schedule estimation in software project?
    4 months ago

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