文档介绍：Chapter 5
Estimating Project Times and Costs
Estimating Projects
Estimating
The process of forecasting or approximating the time and cost pleting project deliverables(估算是对完成项目交付物的时间和成本进行预报和估计的过程).
The task of balancing the expectations of stakeholders and the need for control while the project is implemented(项目估算成了一项平衡主要利益相关者的期望和项目实施时的控制要求的任务).
Why Estimating Time and Cost Are Important
Estimates are needed to support good decisions.
Estimates are needed to determine how long the project should take and its cost.
Estimates are needed to determine whether the project is worth doing.
Estimates are needed to develop cash flow needs.
Estimates are needed to control the project process.
Estimates are needed to schedule work.
Estimates are needed to determine how well the project is progressing.
Factors Influencing the Quality of Estimates
Quality of Estimates
Project Duration
People
Project Structure anization
Padding Estimates
Organization Culture
Other (Nonproject) Factors
Planning Horizon
影响估算质量的因素
Planning Horizon(计划水平)
对当前事件的估算是比较准确的,但对更远事件的估算就困难了。
时间和成本估算的准确性在从概念阶段转入定义工作包的阶段时应该有所提高。
Project Duration (项目周期)
项目周期长会增加估算的不确定性。
people(人员)
准确的估算取决于做出估算的人的技能。
项目成员是否在类似项目上共过事,也会影响有效团队的形成。
人员调动也影响估算,项目增加新人也增加了交流所需的时间。
影响估算质量的因素
Project Structure anization
专一的项目团队可以集中精力从而赢得速度,这一速度也有占有个人全部时间的额外成本。
矩阵式团队可以更为有效地在不同项目间分享人员而降低成本,但由于精力分散,可能会延长项目周期,对协调的要求也高了。
Padding Estimates (填充估算)
在实际情况下,当你被问到时间和成本估算时,我们大多数人倾向于加上一点填充,以增加完成的概率和减少延误的风险。如果项目各个层次上的所有人都加一点填充以减少风险,项目时间长度和成本将大为增加。这一现象使得一些经理或业主提出将时间或成本压缩10%-15%。
Organization Culture (组织文化)
不同组织对填充估算的容忍度不同。
不同组织对估算重要性的看法不一。
Other (Non project) Factors
Estimating Guidelines for Times, Costs, and Resources
Have people familiar with the tasks make the estimate(估算应由对任务最熟悉的一个或多个人做出).
Use several people to make estimates(让多个人来估算).
Base estimates on normal conditions, efficient methods, and a normal level of resources(估算必须基于正常条件、有效方法和正常的资源水平).
Use consistent time units in estimating task times(所有任务的时间估算要有一致的时间单位).
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