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Acknowledgment of Reviewers' Services 对审稿人服务的感谢
Pub Date : 2011-07-01 DOI: 10.1080/1941658x.2011.631853
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引用次数: 0
A Probabilistic Approach to Determining the Number of Units to Build in a Yield-Constrained Process 在产量受限的过程中确定生产单元数量的概率方法
Pub Date : 2011-07-01 DOI: 10.1080/1941658X.2011.585331
Timothy P. Anderson
Many cost estimating problems involve determining the number of units to build in a yield-constrained manufacturing process, when it takes, on average, n attempts to produce m successes (m ≤ n). Examples include computer chips, focal plane arrays, circuit boards, field programmable gate arrays, etc. The simplistic approach to this problem is to multiply the number of units needed, m, by the expected number of attempts needed to produce a single success, n. For example, if a contractor reports that it takes, on average, 10 attempts to build one working unit, and if four such units are needed for a space-borne application, then the simplistic approach would be to plan for 4 × 10 = 40 units, and estimate the cost accordingly. However, if the cost analyst uses the simplistic approach, he or she is likely to be disappointed, as the probability that 40 attempts will actually produce four working units is only about 57%. Consequently, there is a 43% probability that 40 attempts will be insufficient. In fact, if the analyst wants to have, say, 80% confidence that four working units will be available, then he/she should plan for 54 attempts! Obviously, this could have a huge impact on the cost estimate. The purpose of this research is to describe the nature of the problem, to justify modeling the problem in terms of a negative binomial random variable, and to develop the necessary thought process that one must go through in order to adequately determine the number of units to build given a desired level of confidence. This understanding will be of great benefit to cost analysts who are in the position of estimating costs when certain hardware elements behave as described previously. The technique will also be very useful in cost uncertainty analysis, enabling the cost analyst to determine the appropriate probability distribution for the number of units needed to achieve success in their programs.
许多成本估算问题涉及在产量受限的制造过程中确定要制造的单元数量,当平均需要n次尝试才能生产m次成功(m≤n)时。示例包括计算机芯片,焦平面阵列,电路板,现场可编程门阵列等。解决这个问题的简单方法是将所需的单元数m乘以产生单个成功所需的预期尝试数n。例如,如果承包商报告平均需要10次尝试来构建一个工作单元,如果空间应用程序需要4个这样的单元,那么简单的方法将是计划4 × 10 = 40个单元,并相应地估计成本。然而,如果成本分析师使用简单的方法,他或她可能会失望,因为40次尝试实际产生4个工作单元的概率只有大约57%。因此,有43%的概率40次尝试是不够的。事实上,如果分析人员想要有80%的信心,四个工作单元将是可用的,那么他/她应该计划54次尝试!显然,这可能会对成本估算产生巨大影响。本研究的目的是描述问题的本质,证明用负二项随机变量建模问题的合理性,并开发必要的思维过程,以便在给定期望的置信度水平下充分确定要构建的单元数量。当某些硬件元素的行为与前面描述的一样时,这种理解将对成本分析人员有很大的好处。该技术在成本不确定性分析中也非常有用,使成本分析人员能够确定在其计划中获得成功所需的单元数量的适当概率分布。
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引用次数: 1
A Probabilistic Method for Predicting Software Code Growth 预测软件代码增长的概率方法
Pub Date : 2011-07-01 DOI: 10.1080/1941658X.2011.629494
Mike Ross
A significant challenge that many cost analysts and project managers face is predicting by how much their initial estimates of software development cost and schedule will change over the lifecycle of the project. Examination of currently-accepted software cost, schedule, and defect estimation algorithms reveals a common acknowledgment that estimated software size is the single most influential independent variable. Unfortunately, the most important business decisions about a software project are made at its beginning, the time when most estimating is done, and coincidently the time of minimum knowledge, maximum uncertainty, and hysterical optimism. This article describes a model and methodology that provides probabilistic growth adjustment to single-point Technical Baseline Estimates of Delivered Source Lines of Code, for both new software and pre-existing reused software that is sensitive to the maturity of their single-point estimates. The model is based on Software Resources Data Report data collected by the U.S. Air Force and has been used as part of the basis for several USAF program office estimates and independent cost estimates. It provides an alternative to other software code growth methodologies, such as Holchin's and Jensen's code growth matrices.
许多成本分析师和项目经理面临的一个重大挑战是,通过预测他们对软件开发成本和进度的初始估计在项目的生命周期中会改变多少。对当前接受的软件成本、进度和缺陷估计算法的检查揭示了一个共同的认识,即估计的软件大小是最具影响力的独立变量。不幸的是,关于软件项目的最重要的业务决策是在它的开始时做出的,这是完成大多数评估的时候,同时也是知识最少、不确定性最大和歇斯底里乐观的时候。本文描述了一个模型和方法,该模型和方法为交付源代码行的单点技术基线估计提供了概率增长调整,适用于新软件和对单点估计的成熟度敏感的预先存在的重用软件。该模型基于美国空军收集的软件资源数据报告数据,并已被用作美国空军几个项目办公室估算和独立成本估算的基础。它提供了一种替代其他软件代码增长方法的方法,比如Holchin和Jensen的代码增长矩阵。
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引用次数: 0
Statistical Foundations of Adaptive Cost-Estimating Relationships 自适应成本估算关系的统计基础
Pub Date : 2011-01-01 DOI: 10.1080/1941658X.2011.585333
Stephen A. Book, M. Broder, D. Feldman
Traditional development of cost-estimating relationships (CERs) has been based on “full” data sets consisting of all available cost and technical data associated with a particular class of products of interest, e.g., components, subsystems or entire systems of satellites, ground systems, etc. In this article, we review an extension of the concept of “analogy estimating” to parametric estimating, namely the concept of “adaptive” CERs—CERs that are based on specific knowledge of individual data points that may be more relevant to a particular estimating problem than would the full data set. The goal of adaptive CER development is to be able to apply CERs that have smaller estimating error and narrower prediction bounds. Several examples of adaptive CERs were provided in a presentation (Book & Broder, 2008) by the first two authors to the May 2008 SSCAG Meeting in Noordwijk, Holland, and the June 2008 SCEA/ISPA Conference in Industry Hills, CA. This article focuses on statistical foundations of the derivation of adaptive CERs, namely, the method of weighted least-squares regression. Ordinary least-squares regression has been traditionally applied to historical-cost data in order to derive additive-error CERs valid over an entire data range, subject to the requirement that all data points be weighted equally and have residuals that are distributed according to a common normal distribution. The idea behind adaptive CERs, however, is that data points should be “deweighted” based on some function of their distance from the point at which an estimate is to be made. This means that each historical data point should be assigned a “weight” that reflects its importance to the particular estimation that is to be made using the derived CER. This presentation describes technical details of the weighted least-squares derivation process, resulting quality metrics, and the roles it plays in adaptive-CER development.
成本估算关系的传统发展是以“完整”数据集为基础的,这些数据集包括与某一类有关产品有关的所有现有成本和技术数据,例如卫星、地面系统等的组件、子系统或整个系统。在本文中,我们回顾了“类比估计”概念对参数估计的扩展,即“自适应”CERs-CERs的概念,该概念基于单个数据点的特定知识,这些数据点可能比完整数据集更与特定估计问题相关。自适应CER发展的目标是能够应用具有更小估计误差和更窄预测范围的CER。2008年5月在荷兰诺德韦克举行的SSCAG会议和2008年6月在加利福尼亚州工业山举行的SCEA/ISPA会议上,前两位作者在一次演讲(Book & Broder, 2008)中提供了几个自适应CERs的例子。本文侧重于自适应CERs推导的统计基础,即加权最小二乘回归方法。传统上,普通最小二乘回归被应用于历史成本数据,以得出在整个数据范围内有效的加性误差cer,但要求所有数据点的权重相等,并且残差按照共同的正态分布分布。然而,自适应cer背后的思想是,数据点应该根据它们与要进行估计的点之间的距离的某些函数来“加权”。这意味着应该为每个历史数据点分配一个“权重”,以反映其对使用派生CER进行的特定估计的重要性。本演讲描述了加权最小二乘派生过程的技术细节,所产生的质量度量,以及它在自适应cer开发中所起的作用。
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引用次数: 3
Use of Earned Value Management Trends to Forecast Cost Risks 运用挣值管理趋势预测成本风险
Pub Date : 2011-01-01 DOI: 10.1080/1941658X.2011.585335
Roy E. Smoker
This article uses earned value management trend analysis to forecast trends in BAC and BCWP. The resulting equations are then used to solve for the expected month at completion. With the month at completion date in hand, the article uses trend analysis to find the EAC at that month along with the BAC at that month far in the future to solve for VAC. By using variance against a baseline, the article shows how much risk this program will incur by the date at completion. A monthly risk burndown chart is developed to illustrate how the program burns down risk during life of the program. It indicates that the rate of risk burndown may very well be more rapid than the rate of accomplishment of remaining work. The article concludes that program managers would be well advised to require analysis of EVM trends to understand how much additional schedule is being added to a contract with each addition of scope as measured by the increase in BAC over time.
本文采用挣值管理趋势分析来预测BAC和BCWP的趋势。然后用得到的方程来求解完工时的预期月份。有了完成日期的月份,本文使用趋势分析来找到该月的EAC以及该月的BAC,以解决VAC问题。通过对基线使用方差,本文显示了在完成日期之前该程序将产生多少风险。每个月的风险燃尽图表被开发出来,以说明在项目的生命周期中项目是如何燃尽风险的。它表明,风险消耗的速度可能比剩余工作的完成速度要快得多。这篇文章的结论是,项目经理最好需要对EVM趋势进行分析,以了解随着时间的推移,通过BAC的增加来衡量的每次范围的增加,合同中增加了多少额外的进度。
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引用次数: 3
An Application of Data Mining Algorithms for Shipbuilding Cost Estimation 数据挖掘算法在造船成本估算中的应用
Pub Date : 2011-01-01 DOI: 10.1080/1941658X.2011.585336
Bohdan L. Kaluzny, Sorin Barbici, Göran Berg, Renzo Chiomento, Dimitrios Derpanis, Ulf J. Jonsson, R. H. A. D. Shaw, M. Smit, Franck Ramaroson
This article presents a novel application of known data mining algorithms to the problem of estimating the cost of ship development and construction. The work is a product of North Atlantic Treaty Organization Research and Technology Organization Systems Analysis and Studies 076 Task Group “NATO Independent Cost Estimating and its Role in Capability Portfolio Analysis.” In a blind, ex post exercise, the Task Group set out to estimate the cost of a class of Netherlands' amphibious assault ships, and then compare the estimates to the actual costs (the Netherlands Royal Navy withheld the actual ship costs until the exercise was completed). Two cost estimating approaches were taken: parametric analysis and costing by analogy. For the parametric approach, the M5 system (a combination of decision trees and linear regression models) of Quinlan (1992) for learning models that predict numeric values was employed. Agglomerative hierarchical cluster analysis and non-linear optimization was used for a cost estimation by analogy approach void of subjectivity.
本文提出了一种将已知数据挖掘算法应用于船舶研制和建造成本估算问题的新方法。这项工作是北大西洋公约组织研究和技术组织系统分析和研究076任务小组“北约独立成本估算及其在能力组合分析中的作用”的产物。在一次盲测后的演习中,任务小组开始估算荷兰某级两栖攻击舰的成本,然后将估算值与实际成本进行比较(荷兰皇家海军在演习结束前未公布实际舰艇成本)。采用参数分析法和类比法两种成本估算方法。对于参数方法,采用了Quinlan(1992)用于预测数值的学习模型的M5系统(决策树和线性回归模型的组合)。利用聚类层次聚类分析和非线性优化方法进行无主观性的成本估算。
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引用次数: 12
Historical Trend Analysis Analysed 历史趋势分析
Pub Date : 2011-01-01 DOI: 10.1080/1941658X.2011.585329
Dale Shermon
This article describes three alternative approaches to historical trend analysis. First, the study considers the trend over time of the complexities of past systems. This results from the application of a parametric cost model (PRICE H) to the normalisation of historical projects' costs and to the plotting of the complexity over time. Second, the trend over time of the equipment production cost, which has been observed as ‘the cost of successive generations of equipment to continue to rise at above the rate of inflation,’ commonly referred to as ‘Defence equipment cost growth.’ Finally, an analysis of technology over time through the application of multi-variable, forward step-wise regression (true concepts methodology)—one of the variables in the regression analysis being the cost residual versus time representing the cost of technology growth. The article describes the advantages and disadvantages of each historical trends analysis method. The research study indicates when each method might be applicable and in what circumstances it is dangerous to consider their usage. A case study has been used to consider the effect and accuracy of each of the methods. This review has considered the historical trend for a particular system and predicted the future cost of a possible acquisition. The objective of the study is to stimulate discussion amongst the cost community as to the usage of historical trends analysis, a common term that has not matured in many ways. The historical trends analysis technique is transferable and equally applicable to commercial or government organisations wishing to predict their own costs.
本文描述了历史趋势分析的三种替代方法。首先,该研究考虑了过去系统复杂性随时间变化的趋势。这是由于将参数化成本模型(PRICE H)应用于历史项目成本的标准化和复杂性随时间的绘图。第二,随着时间的推移,设备生产成本的趋势,被观察为“连续几代设备的成本将继续以高于通货膨胀率的速度上升”,通常被称为“国防设备成本增长”。最后,通过应用多变量、前向逐步回归(真概念方法)对技术随时间的变化进行分析——回归分析中的一个变量是代表技术增长成本的剩余成本与时间的关系。文章描述了每种历史趋势分析方法的优缺点。研究表明,每种方法何时可能适用,以及在什么情况下考虑使用它们是危险的。通过一个案例研究来考虑每种方法的效果和准确性。该审查考虑了特定系统的历史趋势,并预测了可能收购的未来成本。这项研究的目的是激发成本界对历史趋势分析的使用进行讨论,这是一个在许多方面尚未成熟的常用术语。历史趋势分析技术是可转让的,同样适用于希望预测自己成本的商业或政府组织。
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引用次数: 2
Acknowledgment of Reviewers' Services 对审稿人服务的感谢
Pub Date : 2011-01-01 DOI: 10.1080/1941658x.2011.585337
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引用次数: 0
Cost Risk as a Discriminator in Trade Studies 成本风险在贸易研究中的区别
Pub Date : 2010-11-01 DOI: 10.1080/1941658X.2010.10462234
Stephen A. Book
Abstract Prior to formal program initiation, analysts typically undertake trade studies to investigate which of several candidate architectures or designs can best provide a desired capability at minimum cost. The various candidates, however, typically differ significantly in risk and uncertainty as well as in cost, but members of the government or industry trade-study team do not have the time and the candidate solutions usually aren't sufficiently detailed at this stage to allow a thorough risk analysis to be conducted. Yet, those differences in risk and uncertainty, as well as in cost, should be taken into account to the extent possible during the trade-study decision process. Because timeliness and simplicity are key requirements of analyses undertaken in support of trade studies, what usually happens is that a “point” cost estimate, or perhaps a 50%-confidence estimate, is established for each candidate, and the go-ahead decision is made based on that estimate. A nagging question remains: “What if Candidate A, the lower-cost option based on those estimates, faces risk issues that make its 80th-percentile cost higher than that of Candidate B?” In other words, Candidate B would be the lower-cost option if the cost comparison were made at the 80% confidence level. This situation is classic, where the decision maker must choose between a low-cost, high-risk option and a high-cost, low-risk option. This article offers a methodology that allows the program manager to take account of all risk scenarios by making use of all cost percentiles simultaneously, namely the entire cost probability distribution of each candidate not simply the point estimate or the 80% confidence cost. As it turns out, the expression of system cost in terms of a lognormal or simulation-generated probability distribution makes it possible to estimate the probability that each candidate will turn out to be the least costly of all the options, and probabilities of that kind are the basis on which an informed decision can be made.
在正式的程序启动之前,分析人员通常进行贸易研究,以调查几种候选架构或设计中哪一种能够以最小的成本最好地提供所需的能力。然而,不同的备选方案在风险和不确定性以及成本方面通常存在很大差异,但政府或行业贸易研究团队的成员没有时间,在这个阶段,备选方案通常不够详细,无法进行彻底的风险分析。然而,在贸易研究决策过程中,应尽可能考虑到风险和不确定性以及成本方面的差异。因为时效性和简洁性是支持贸易研究的分析的关键要求,通常发生的情况是为每个候选人建立一个“点”成本估计,或者可能是50%置信度的估计,并根据该估计做出前进的决定。一个挥之不去的问题仍然存在:“如果候选A——基于这些估算的成本较低的选项——面临风险问题,导致其第80百分位成本高于候选B,该怎么办?”换句话说,如果在80%的置信水平上进行成本比较,候选人B将是成本较低的选项。这种情况很典型,决策者必须在低成本、高风险的选择和高成本、低风险的选择之间做出选择。本文提供了一种方法,允许项目经理同时利用所有的成本百分位数来考虑所有的风险场景,即每个候选项目的整个成本概率分布,而不仅仅是点估计或80%置信度成本。事实证明,用对数正态分布或模拟生成的概率分布来表示系统成本,可以估计出每个候选方案最终成为所有选项中成本最低的方案的概率,而这种概率是做出明智决策的基础。
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引用次数: 4
The Probable Lowest-Cost Alternative According to Borda 根据Borda的说法,这可能是成本最低的替代方案
Pub Date : 2010-11-01 DOI: 10.1080/1941658X.2010.10462232
N. Hulkower
Abstract Exact Probabilities by Simulation, a method introduced by Book (2010a) for determining which candidate in a trade study is the probable lowest-cost alternative, is extended to ensure that all available data generated are used. The Borda Count, the only “non-dictatorial” positional voting method that satisfies the criteria for a rational decision procedure while using the complete information, is then applied to determine the rank ordering of the alternatives. The extended method, called “Exact Probabilities by Simulation with Borda,” gives the most reliable outcome; it yields a ranking that easily blends with those based on other criteria to select the best alternative in a trade study.
Book (2010a)引入的精确概率模拟方法用于确定贸易研究中哪个候选方案可能是成本最低的替代方案,该方法被扩展到确保使用所有生成的可用数据。Borda Count是唯一的“非独裁”位置投票方法,它在使用完整信息的情况下满足理性决策过程的标准,然后应用它来确定备选方案的排名顺序。这种扩展的方法被称为“Borda精确概率模拟”,它给出了最可靠的结果;它产生的排名很容易与基于其他标准的排名混合在一起,以在贸易研究中选择最佳替代方案。
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引用次数: 1
期刊
Journal of Cost Analysis and Parametrics
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