The effect of systemic errors on optimal project buffers
The effect of systemic errors on optimal project buffers
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DOI：
10.1016/j.ijproman.2004.12.004
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发表时间：
2005-05
影响因子：
8
通讯作者：
D. Trietsch
中科院分区：
文献类型：
--
作者：
D. Trietsch
在项目管理中设置时间或成本缓冲的现有数学模型假设项目活动在统计上是独立的。这导致了一个非常违反直觉和破坏性的结论，即对于具有长活动链的项目，项目缓冲应该相对可以忽略不计。我们提出了一个模型，考虑了由估计偏差引起的活动之间的统计依赖性。我们表明，如果需要相对较高的服务水平，这将在缓冲区上施加一个正的下限，作为估计项目持续时间或预算的基于数据的部分。我们还介绍了一种收集数据和估计实现模型所需参数的新方法。与传统PERT相比，这种方法给决策者带来的负担更小：它们为平均值提供单点估计，而方差元素和偏差校正则使用历史数据以电子方式计算。
Existing mathematical models for setting buffers for time or cost in project management assume that project activities are statistically independent. This leads to a highly counterintuitive and damaging conclusion that project buffers should become relatively negligible for projects with long chains of activities. We present a model that considers the statistical dependence between activities caused by estimation bias. We show that if relatively high service levels are desired, this imposes a positive lower bound on the buffer as a data-based fraction of the estimated project duration or budget. We also introduce a new approach for collecting data and estimating the parameters necessary to implement the model. This approach places a smaller burden on decision makers than traditional PERT: they provide single point estimates for means, while variance elements and bias correction are computed electronically using historical data.