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Construction Estimating and

Cost Management


3.1Introduction 简介
3.1简介 简介

3.1.1 Text
3.1.1 文本

1.Project Cost System 项目成本系统

During the design phase of a construction project, the project costs are continuously approximated and reviewed following each design change to ensure that they will not exceed the owner's budget. This working budget is generally referred to as the engineer's or architect's estimate. Upon design completion, the field cost-control system is initiated by making a final,detailed cost estimate of the entire work. The construction contractor or another party who will be directly involved in the field operations normally prepares this “ contractor's estimate ”. The contractor's estimate is then reduced to a working construction budget and forms the basis of the construction cost-control system. During the construction process, cost accounting methods are used to retrieve actual construction expenses from ongoing construction operations. This information is then used for cost-control purposes on the current project and for estimating the cost of future projects. Additionally, the cost system provides considerable information pertinent to project financial control.

2. Classification of Cost Estimates 成本估算分类
2. Classification of Cost Estimates 成本估算分类

There are many ways of classifying building cost estimates. The most significant of these are the degree of project definition, the end usage of the estimate, and the estimate generating methodology.The first classification, the degree of project definition, is based upon the percentage of completed architectural and engineering designs It defines available input


Chapter 3 Construction Estimating and Cost Management 建设工程造价和成本管理

information to the estimator. The second classification, the end usage of the estimate,is based on available data progress and covers conceptual estimates for investment feasibility,and studies funding authorization, budgets, and contractor detail estimates for lump-sum bidding.The third classification, the estimate generating methodology, is based on processes employed to forecast building costs that are stochastic and deterministic.

3.Accuracy Range 精度范围

Related to various types of building cost estimates, a prudent owner or contractor must associate the expected accuracy range”. The estimate accuracy is an indication of the degree to which the future final (true) cost of a building varies fromi the estimate prepared earlier. Accuracy is usually expressed as a positive or negative percentage range surrounding an estimated future cost. Table 3-1 provides a general overview of construction cost estimates with three methods.
与各种类型的建筑成本估算有关,谨慎的业主或承包商必须将“预期精度范围”联系起来。估算精度表示建筑物的未来最终(真实)成本与先前准备的估算不同程度。准确性通常表示为围绕估计未来成本的正百分比或负百分比范围。表 3-1 提供了使用三种方法估算的施工成本估算的一般概述。

Table 3-1 Three tyes of construction cost estimating methods
表3-1 三大工程造价估算方法

Type of Estimate

Construction Development

Expected Percent Error


Programming and schematic design


Design development


Plans and specification

4. Approaches to Cost Estimation 成本估算方法
4. Approaches to Cost Estimation 成本估算方法

Some of the approaches commonly used to prepare estimates include:

Function estimate. This analysis is based on the estimated expenditure per unit of use,such as cost per patient, student, seat, or car space. Construction expense may also be approximated as the average outlay per unit of a plant's manufacturing or production capacity.These parameters are generally used as a method of quickly defining facilities costs at the inceptiont of a project when only raw marketing information is known, such as the number of patients that a planned hospital will hold. This broad method of developing costs can also provide a powerful check on more detailed estimates once they have been generated.

Empirical cost inference. Empirical estimation of cost functions requires statistical techniques which relate the cost of constructing or operating a facility to a few important characteristics or attributes of the system. The role of statistical inference is to estimate the best parameter values or constants in an assumedi cost function. Usually, this is accomplished by means of regression analysis techniques.

Unit costs for bill of quantities. A unit cost is assigned to each of the facility components or tasks as represented by the bill of quantitiest. The total cost is the summation of the products of the quantities multiplied by the corresponding unit costs. The unit cost method is straightforward in principle but quite llaborlousi in application. The initial step is to break down or disaggregate a process into a number of tasks. Collectively, these tasks must be completed for the construction of a facility. Once these tasks are defined and quantities representing these tasks are assessed, a unit cost is assigned to each and then the total cost is determined by summing the costs incurred in each task. The level of detail in decomposing


into tasks will vary considerably from one estimate to another.

Allocation of joint costs. Allocations of cost from existing accounts may be used to develop a cost function of an operation. The basic idea in this method is that each rexpenditure item can be assigned to particular characteristics of the operation. Ideally, the allocation of joint costs should be causally related to the category of basic costs in an allocation process. In many instances,however, a causal relationship between the allocation factor and the cost item cannot be identified or may not exist. For example,in construction projects, the accounts for basic costs may be classified according to: ①labour; ②material;③construction equipment; construction supervision; general office overhead. These basic costs may then be allocated proportionally to various tasks which are isubdivisions of a project.

5.Preliminary Cost Estimates 初步成本估算
5.Preliminary Cost Estimates 初步成本估算

Preliminary estimates of future construction expenditures, made during the project planning and design phases, are necessarily approximate because they are compiled before the project is completely defined. Making such conceptual estimates is an art quite different from determining the final detailed estimate of construction costs. Fundamentally, all conceptual price estimates are based on some system of gross unit costs obtained from previous construction work. These unit costs are extrapolated forward in time to reflect current market conditions, project location,and the particular character of the job presently under consideration.

6.Final Cost Estimate 最终成本估算

The final cost estimate of a project is prepared when finalized working drawings and specifications are available. This detailed estimate of construction expense is based on a complete and detailed survey of work quantities required to accomplish the work. The process involves the identification,compilation, and analysis of the many items of cost that will enter into the construction process. Such estimating, which is done before the work is actually performed,requires careful and detailed study of the design documents, together with an intimate knowledge of the prices, availability, and characteristics of materials, construction equipment,and labour.

7.Quantity Survey 工料测量

The first step in preparing the final estimate of a construction project is the preparation of a quantity survey. This survey is simply a detailed compilation of the nature and quantity of each work type required. Taking off quantities is done in substantial detail, with the project being divided into many different work types or classifications. In the case of heavy civil projects where lunit-price bidding is involved, even though the architect engineer icustomarily provides estimated quantities of each bid item with the bidding documents, a detailed quantity survey is still required. A basic reason for making a quantity survey for unit-price bidding is that most bid items cannot be priced without breaking the work down into smaller subdivisions.Another reason is that the architect-engineer's quantity estimates are specifically stated to be approximations only. Finally, for any estimate, developing the quantity survey provides the estimator with the intimate familiarity of job requirements so vital to realistic project pricing. The estimator takes the dimensions and numbers of units of each work type from the design

3 Construction Estimating and Cost Management 建设工程造价和成本管理


drawings, enters them on quantity sheets, and extends them into totals. Quantities estimated by the architect-engineer and by the bidding contractors do not always check; at times,the differences can be substantial. However, for such a relatively precise work package,it is reasonable to assume that agreement of the quantity figures will be relatively close in all cases.

3.2Basic Elements of Cost Estimation 成本估算的基本要素

3.2.1 Text
3.2.1 文本

1.Material Costs 材料费
1.Material Costs 材料费

It is customary for the contractor to solicit and receive specific price quotations for most of the materials required by the job being priced. Written quotations for special job materials are desirable so that such important considerations as prices, freight charges, taxes, delivery schedules, and guarantees are explicitly understood. Most material suppliers tender their quotations on printed forms that include istipulations pertaining to terms of payment and other considerations. When material costs are entered on the summary sheets, they must all have a common basis, for example, delivered to the job site and without sales tax. Prices as entered will ordinarily include freight, drayage,storage, and inspection. It is common practice to enter material prices without tax, adding this as a lump-sum amount on the final recap sheet.It is not unusual in some types of projects for the owner to provide certain materials to the contractor for use on the project. In such a case, contractors need not add this material price



into their estimates. However, all other charges associated with the material, such as handling and installation expense, must be included.

2.Labour Costs 人工费
2.Labor Costs 人工费

The real challenge in pricing construction work is determining labour and equipment expenditures. To do an acceptable job of establishing these outlays, the estimator must make a complete and thorough job analysis, maintain a comprehensive library of unit costs and production rates from past projects, and obtain advance decisions regarding how construction operations will be conducted. Contractors differ widely in how they estimate labour costs.Some choose to include all elements of labour expense in a single hourly rate. Others evaluate direct labour cost separately from indirect cost. Some contractors compute regular and overtime labour costs separately, while others combine scheduled overtime with straight time to arrive at an average hourly rate . Some evaluate labour charges using production rates; others use labour unit costs. There are usually good reasons for a contractor to evaluate its labour expense as it does, and there certainly is no single correct method that must be followed.

3.Indirect Labour Costs 间接人工费
3.Indirect Labor Costs 间接人工费

Direct labour cost is determined from the workers' basic wage rates,that is, the hourly rates used for payroll purposes. Indirect labour costs are those expenses that are additions to the basic hourly rates and that are paid by the employer. Indirect labour expense involves various forms of payroll taxes, insurance, and a wide variety of employee fringe benefits.Indirect labour costs are isubstantial in amount, often constituting a 35% to 55% addition to direct payroll expenses. For estimating purposes, total labour outlay can be computed in one operation by using hourly labour rates, which include both direct and indirect costs. However,this procedure may not interrelate well with labour cost accounting methods. For this reason,direct and indirect labour charges often are computed separately when job prices are being estimated. One commonly used scheme is to add a percentage rallowance for indirect costs to the total direct labour expense, either for the entire project or for each major work category.

4. The Cost of Heavy Equipment 重型设备成本
4. The Cost of Heavy Equipment 重型设备成本

Equipment costs, like those of labour, are difficult to evaluate and price with precision.Equipment laccounts for a substantial proportion of the total construction expense of most engineering projects but is less significant for buildings. When the nature of the work requires major items of equipment, such as rearth-moving machinesi, concrete plants, and truck cranes, detailed studies of the associated costs must be made. Expenses associated with minor equipment items, such as ipower toolsi,concrete vibrators,and concrete buggies,are not normally subjected to detailed study.

A standard expense allowance for each such item required is included, usually based on the duration it will be required on the job. The cost of small tools, wheelbarrowsi,water hoses,rextension cords, and other such items are covered by a llump-sumi allowance sometimes obtained as a small percentage of the total labour cost of the project. Every construction project manager should keep in mind the fact that efficient use of heavy equipment on a job is paramount to attaining cost and schedule objectives. Early project planning should include


Chapter 3 Construction Estimating and Cost Management 建设工程造价和成本管理

analysis of exactly what equipment is best for the job and how this equipment is to be acquired:by using the company's own equipment, purchasing new equipment, or renting or leasing the equipment. Project managers do well to remember that company-owned equipment is not “free equipment”. It represents an investment of capital by the company, and its use on the project should show a return on investment to the company for the time it is on the job.

5.Bids from Subcontractor 分包商报价

If the prime contractor intends to subcontract portions of the project to specialty contractors,the compilation and analysis of subcontractor bids is an important aspect of making up the final project estimate. Bids from subcontractors sometimes contain qualifications or stipulate that the general contractor is to be responsible for providing the subcontractor with certain job site services, such as hoisting, electricity and water, storage facilities for materials, and many others. Before estimators can identify the low subcontractor bid (subbid) for any particular itemof work, they must analyse each bid received to determine exactly what each such proposal includes and does not include. In any event, the contractor must compile its own cost of doing the work involved and normally will be interested only in those subbids whose amounts are less than its own estimated direct cost. When the general contractor receives a subbid whose amount is less than its own estimated direct outlay for doing the same work, it cannot accept such a subbid until consideration is given to several factors. The general contractor must remember that it is completely responsible by contracting with the owner for all subcontracted work as well as that performed by its own forces.

6.Overhead 日常管理费

Overhead or indirect expenses are outlays that are incurred in achieving project completion but that do not apply directly to any specific work item. Two kinds of overhead pertain to a contractor's operations: project overhead and office overhead.

Project overhead, also referred to as job overheadi or field overhead, pertains to indirect field expenses that are chargeable directly to the project. Some contractors figure their job overhead outlay as a percentage of the total direct job cost; common values for the job overhead allowance range from 5% to 15% or more. The use of percentages when computing field overhead is not generally considered to be good estimating practice because different projects can and do have widely varying job overhead requirements. The only reliable way to arrive at an accurate estimate of project overhead is to make a detailed analysis of the particular demands of that project. It is standard estimating procedure to list and price each item of indirect expense on a separate overhead sheet.
项目间接费用,也称为作业间接费用或现场间接费用,与直接计入项目的间接现场费用有关。一些承包商将他们的工作间接费用支出计算为直接工作总成本的百分比;工作间接费用津贴的常见值范围为 5% 至 15% 或更多。在计算现场开销时使用百分比通常不被认为是良好的估算做法,因为不同的项目可以而且确实具有很大不同的工作开销要求。准确估计项目开销的唯一可靠方法是对该项目的特定需求进行详细分析。标准的估算程序是在单独的间接费用表上列出每个间接费用项目并为其定价。

Home office overhead is made up of charges that are incurred in support of the overall company construction program and that cannot be charged to any specific project. For this reason, home office overhead is normally included in the job estimate as a percentage of the total estimated project expense. The allowance for office overhead can be added as a separate line item in the cost estimate, or a suitable“markup” percentage can be applied, or a fee can be established that includes both home office overhead and profit. The total of this overhead expense usually ranges from 2% to 8% of a contractor's annual business volume. An allowance
家庭办公室间接费用由支持整个公司建设计划而产生的费用组成,不能对任何特定项目收取。因此,家庭办公室的间接费用通常包含在工作估算中,占估计项目总费用的百分比。办公室间接费用的备抵可以作为单独的行项目添加到成本估算中,或者可以应用适当的“加价”百分比,或者可以确定包括家庭办公室间接费用和利润的费用。这种间接费用的总和通常在承包商年度业务量的 2% 到 8% 之间。津贴



for such indirect expense must be included in the cost estimate of each new project.


On competitively bid projects, markup or margin is added at the close of the estimating process and is an allowance for profit plus possibly other items, such as office overhead and contingency. Regarding contingency as a separate component of markup is a matter of management philosophy. The profit included in a job bid represents the minimum acceptable return on the contractor's investment. Return on investment is a function of risk, and greater risk calls for a greater profit allowance in the proposal. Whether recognition of risk is in the form of a higher profit percentage or the inclusion of a contingency allowance seems to be a matter of personal preference.

Markup,which may vary from 5% to more than 20% of the estimated project cost,represents the contractor's considered appraisal of a whole series of imponderables that may influence its chances of being the low bidder and of its making a reasonable profit if it is. Many factors must be considered in deciding a markup figure, and each can have an influence on the figure chosen. The size of the project and its complexity, its location, provisions of the contract documents, the contractor's evaluation of the risks and difficulties inherent in the work, the competition, the contractor's desire for the work, the identity of the owner and/or the architect-engineer,and other intangibles can have a bearing on how a contractor marks up a particular job.

3.3Cost Management 成本管理


Cost management is the process which is necessary to ensure that the planned development of a design and procurement of a project is such that the price for its construction provides value


Chapter 3Construction Estimating and Cost Management 建设工程造价和成本管理3
Chapter 3Construction Estimating and Cost Management 工程造价和成本管理3

for money (VFM) and is within the limits anticipated by the client. Estimating and cost management should be treated as the integrated principal component of a process composed of the following revolving phases:developing the estimate, establishing the budget,managing the inevitable changes to the project,and making modifications to the estimate.
为了金钱 (VFM),并在客户预期的范围内。估算和成本管理应被视为由以下循环阶段组成的过程的综合主要组成部分:制定概算、制定预算、管理项目不可避免的变化以及对概算进行修改。

1.The Construction Cost Cycle 工程成本周期
1.The Construction Cost Cycle 工程成本周期

The cost cycle for a construction project begins with an estimate based upon cost and production data specific to the company and developed on previous projects. This historic cost database is highly proprietary and greatly valued by the company. Based on actual production records and costs from previous jobs, it gives the company the best basis for pricing new work so that it can be competitive and yet protected as much as possible from underprizing work.

The estimate, discussed above, is a cost-based model of the project, just as the drawings are a graphical model of the project, the speciications are a verbal model of the project, and the schedule is a time-based model of the project. As the project progresses, this cost model is modified to reflect its purpose at any given point. The initial estimate is developed so that the company will know how much it will cost to complete the project. The initial estimate is then adjusted and used as a basis for negotiating or bidding the project. The objective of this proposal or bid estimate is to successfully enter into a contract to execute the job. Once the job is under contract, the owner will want a schedule of values from the contractor. The term schedule in this case does not refer to the time-based models that have been discussed previously in the book but, rather, to a listing of costs to be used as a basis for billing throughout the project. Since the schedule of values is the basis for periodic billings, as the project manager develops the schedule of values, the estimate will be tailored in order to design a more advantageous cash flow. Another modification to the project estimate results in the contractor's project budget. The project manager, often working with the field supervisor, will refine the initial estimate based on the actual contract amount that was negotiated and on how the project team anticipates investing that amount. It is at this point that the project team has the opportunity to review the initial estimate in details and reallocate funds from those work items that they feel they can construct more efficiently than estimated to cover shortfalls in work items that they anticipate to be more costly to build than estimated. This budget then becomes the basis for the cost-control system that will be used to track costs throughout the project.
如上所述,估算是基于成本的项目模型,就像图纸是项目的图形模型一样,规格是项目的口头模型,而进度计划是基于时间的项目模型。随着项目的进展,此成本模型将被修改,以反映其在任何给定点的用途。制定初步估算是为了让公司知道完成项目需要多少钱。然后对初步估算进行调整,并将其用作项目谈判或投标的基础。该提案或投标估算的目的是成功签订合同以执行工作。一旦工作签订合同,业主将需要承包商提供价值表。在这种情况下,术语“进度”并不是指本书前面讨论过的基于时间的模型,而是指用作整个项目计费基础的成本列表。由于分项表是定期计费的基础,因此在项目经理制定分项表时,将对估算进行调整,以设计更有利的现金流量。对项目估算的另一项修改导致承包商的项目预算。项目经理通常与现场主管合作,将根据谈判的实际合同金额以及项目团队预计如何投资该金额来完善初步估算。正是在这一点上,项目团队有机会详细审查初步估计,并从他们认为可以比估计更有效率地构建的工作项中重新分配资金,以弥补他们预计建造成本高于估计的工作项的不足。 然后,该预算成为成本控制系统的基础,该系统将用于跟踪整个项目的成本。

2.Objectives of a Cost System 成本系统的目标

The project cost system is designed to accomplish two important objectives. One is to develop labour and equipment production information that is useful to project management and supervision in controlling construction costs and maintaining them within the budget. The second is to develop labour and equipment cost information in a form suitable to support the accurate estimating of the cost of future work. The ability to estimate construction costs accurately and then to execute work within the budget established by that estimate is a key element in the success of any construction firm. Regardless of the type of contract arrangements agreed on with the owner, it is important that the contractor exercise the maximum contol possible over its field costs during the construction period. A functioning and reliable cost system


pplayssawxitalsrale in the proper management of a construction project.
pplayssawxitalsrale 在建筑项目的适当管理中。

3.Project Cost Control 项目成本控制

As previously indicated, project cost control actually begins with the preparation of the original oost estimate and the subsequent construction budget. Keeping within the cost budget and knowing when and where job costs are deviating are two factors that constitute the key to a profitable operation. As the work proceeds in the field,icost accounting methods are applied to determine the actual costs of production. The costs as they actually occur are continuously oompared with the budget. In addition to monitoring current expenses, periodic reports are prepared that forecast final project costs and compare these predicted costs with the established budget. Fleld costs are obtained in substantial details because this is the way jobs are originally estimated and also because excessive costs in the field can be corrected only if the exact cause of the overrun can be isolated.

Establishing cost overruns is not especially helpful unless the factors leading to the overrun can be distilled and targeted for improvement. Cost reports are prepared at regular time intervals. These reports are designed to serve as management=by=exception devices, making it possible for the contractor to determine the cost status of the project and to pinpoint those work classifications where expenses are excessive. In this way, management consideration is quickly focused on those job areas that need attention. Timely information is required if effective action against ccost overruns is to be taken. Detection of excessive costs once the work is finished leaves the contractor with no possibility of taking corrective action.
除非能够提炼出导致超支的因素并有针对性地进行改进,否则确定成本超支并不是特别有用。定期编制成本报告。这些报告旨在用作 management=by=exception 设备,使承包商能够确定项目的成本状态并确定费用过高的工作分类。通过这种方式,管理层的考虑迅速集中在那些需要注意的工作领域。如果要采取有效行动防止成本超支,就需要及时提供信息。一旦工作完成,检测到成本过高,承包商就不可能采取纠正措施。

4.Project Cost Accounting 项目成本核算

Project cost accounting is the key ingredient in the project cost system. It provides the basic data required for both cost control and estimating. Cost accounting differs substantially from financial accounting, however. Cost accounting relates solely to determining the detailed makeup of productivity and costs associated with the production of a construction product in the field, including the necessary overhead expense. Project cost accounting is not separate from the contractor's general system of accounts; rather, it is an elaboration of the basic project expense accounts. Cost accounting involves the continuous determination of productivity and cost data, the analysis of this information, and the presentation of the results in summary form. It is thus seen that project cost accounting differs from the usual accounting routines in that the information gathered, recorded, and analysed is not entirely in terms of dollars and cents, Construction cost accounting is necessarily concerned with costs, but it is also concerned with man-hours, equipment-hours, and the amounts of work accomplished. The systematic and regular checking of costs is a necessary part of obtaining reliable, time-averagel production information. A system that evaluates field performance only intermittently in the form of occasional spot checks does not provide trustworthy feedback information, either for cost control or for estimating purposes.

5. Cost Accounting Reports 成本核算报告

Summary labour and equipment cost reports must be compiled often enough so that excessive project costs can be detected while there is still time to remedy them. Cost report

Chapter Construction Estimating and Cost Manageen T尘曰在

intervals are very much a function of project size, duration, and nature of the work, and the type of construction contract involved. Obviously, some kind of balance must be struck between the cost of generating the reports and the value of the management information received. Often, daily cost reports are prepared on complex projects involving multiple shifts.Most jobs, however, do not profit from such frequent cost reporting. Some very large projects involving relatively uncomplicated work classifications find monthly or even longer intervals to be satisfactory. For most construction projects, however, cost reports are needed more often than this.

6.Earned Value Management System 挣值管理系统
6.挣值管理系统 挣值管理系统

The Earned Value Management System (EVMS), sometimes referred to as Cost/Schedule Control Systems Criteria, is an rextension of the time-cost envelope principle. Originally developed by industrial engineers to gauge plant output performance, EVMS compares the physical work accomplished to date with both the actual cost expenditure and the planned work to be accomplished. This three-dimensional comparison determines the earned value on a project and forms the basis for a more accurate projection of final project cost than can be calculated simply by contrasting actual costs with planned funds. Earned value calculations and project performance projections are based on three fundamental variables:
挣值管理系统 (EVMS),有时也称为成本/进度控制系统标准,是时间成本包络原则的再扩展。EVMS 最初由工业工程师开发,用于衡量工厂的输出性能,将迄今为止完成的物理工作与实际成本支出和计划要完成的工作进行比较。这种三维比较确定了项目的挣值,并为更准确地预测最终项目成本奠定了基础,而不是简单地将实际成本与计划资金进行对比。挣值计算和项目绩效预测基于三个基本变量:

(1)Budgeted cost of work performed (BCWP). The cumulative budgeted value of all of the work activities accomplished to date. It is analogous to the budgeted cost of the work accomplished and is calculated by adding up the cost budgets assigned to each of the schedule activities accomplished as of the present date. The BCWP is therefore the“earned value” of the project to date.
(1)已完成工作预算的成本 (BCWP)。迄今为止完成的所有工作活动的累计预算价值。它类似于已完成工作的预算成本,其计算方法是将分配给截至当前日期已完成的每项计划活动的成本预算相加。因此,BCWP是该项目迄今为止的“挣值”。

(2)Budgeted cost of work scheduled (BCWS) . The cumulative planned value of all of the work activities accomplished in the baseline schedule to date. As with time-cost envelopes,this can be any value between the early-start valuation icurve and the late-start valuation curve but is most often taken to be the valuation calculated by accumulating planned progress against the early dates in the schedule.
(2)预算工作计划成本 (BCWS)。迄今为止在基线计划中完成的所有工作活动的累计计划值。与时间成本包络一样,这可以是早期开始估值曲线和后期开始估值曲线之间的任何值,但通常被认为是通过累积计划进度与计划中的早期日期进行累积来计算的估值。

(3) Actual cost of work performed (ACWP). The cumulative actual cost for work completed to date. It was referred to as the actual cost to date and is simply the raccrued total cost for all work accomplished through the present date.

By comparing the BCWP, BCWS, and ACWP, the project manager can calculate to-date variances in schedule, forecasted schedule slippage at project completion, to-date variances in cost, and any forecasted cost over expenditures. The cumulative cost variance(CV) on the project is calculated by subtracting the ACWP from the BCWP. Similarly, cumulative schedule variance (SV) is calculated by subtracting the BCWS from the BCWP. This variance is calculated as a currency value rather than as a division of time. This is because it measures the difference between the planned value scheduled and the earned value achieved, with value measured a a currency.
通过比较 BCWP、BCWS 和 ACWP,项目经理可以计算进度的当前差异、项目完成时的预测进度滑点、成本的当前差异以及任何预测的成本与支出之比。项目的累积成本差异 (CV) 是通过从 BCWP 中减去 ACWP 来计算的。同样,累积计划方差 (SV) 是通过从 BCWP 中减去 BCWS 来计算的。此差异是按货币值计算的,而不是按时间划分计算的。这是因为它衡量计划价值与实现的挣值之间的差额,价值衡量为一种货币。

In order to normalize the measurement of project performance effectively,schedule an cost variances can be converted intounitless indices used to benchmark projects of differin


volumes or to forecast completion performance using interim measurements taken at regular updates during the project. The cost performanceindex (CPI) and the schedule performance index (SPI) are calculated in this way:
数量或使用项目期间定期更新的临时测量来预测完工绩效。成本绩效指数 (CPI) 和进度绩效指数 (SPI) 的计算方式如下:

Therefore, an index value of greater than 1 indicates positive performance against plan,whereas a value of less than 1 demands management intervention.
因此,指数值大于 1 表示对计划的积极绩效,而小于 1 的值则需要管理层干预。