Collection of construction cost data
Workbook modified bills of quantity format
Introduction
DMS
International, Inc. was requested to assist the World Bank with creating a
method of collecting construction cost data from member countries throughout
the world to assist with economic studies.
The task of data collection is a difficult procedure and can be prone to
wide variations. Based upon our experience as construction cost consultants,
estimators and quantity surveyors we chose to develop a data collection method
based upon a workbook format. Our
workbook defines construction line items and quantities for relativity simple
building types. In fact, four building types have been chosen:
- Residential house
- Warehouse
- Road
- Office building
The workbooks
would be sent to member countries to be completed by local contractors,
estimators or quantity surveyors. When
completed the data would be collected and analyzed by the World Bank as part of
its overall economic study.
Before we explain further about our workbook format and design,
reference must be made to previous studies and methods of construction cost
data collection. One comprehensive
review of past practices has been completed by Dubner and McKenzie1. This detailed study compares various methods
and documents the advantages and disadvantages of each method. The method that provides the best opportunity
for data collection was noted as the Bills of Quantity (BOQ) method. This method appears to have advantages over
the other methods but yet even with the BOQ method some potential pitfalls exist.
A
BOQ is basically a listing by trade of certain construction components that
make up the total project. The project may be an office building or a
warehouse. The BOQ documents quantities
for each element of the building type such as cubic meters of concrete
foundations or square meters of roofing material. BOQ’s are used frequently to assist in
developing tenders or bids for projects throughout the world. The BOQ may be provided by an independent
party or in house by the bidding contractor.
Once the quantity of concrete footing is known a unit price to cover for
material, labor and equipment is applied to develop the cost of each line item
or component. The total project is
basically a summation of all the individual line items. Various levels of sophistication in terms of
measurement detail and description exist with BOQ’s but the same principals
apply. The paper prepared by Dubner and McKenzie1,
suggests that the BOQ method offers the best opportunity for data collection,
though they suggest issues that must be dealt with to allow data collection to
prove more successful than in the past.
The issues highlighted were:
- Interpretation of specifications
- Expertise to price BOQ
- Applicability of specifications to local
design criteria
- Over sophistication and requirement to
price detail project work break downs
Silke
Stapel2 also highlights various issues with cost data collection
along the similar lines as Dubner and McKenzie1. Stapel 2 is part of Eurostat, an
organization that has actually performed data collection on behalf of EU member
states. Part of the Eurostat data
collection used detailed Bills of Quantities.
Stapel
2 along similar lines as Dubner and McKenzie1 noted some
issues such as:
- Data collection was expensive in terms
of resources required to implement system
- Bills of Quantities adopted by Eurostat
appear too cumbersome in terms of level of detail and sophistication
It
would appear that the Eurostat data applies to advanced Countries in terms of
construction management and professional expertise. The Eurostat surveys collect prices for about
15 Bills of Quantities. The typical
Bills of Quantities could have up to 1000 line items.
A Modified Approach
In
our approach, we have attempted to incorporate improvements into the workbook approach
such as:
- Provide a consistent quantity of
materials and line items to price
- Line items are simple and comprise basic
building materials common to most countries (e.g. cubic meters of
footings)
- Quantities and line items reflect
approximate quantities according to a trade break down. The trade breakdown adopted reflects
American Institute of Construction Specifiers, 16 divisions trade
format. The trade format reflects a
traditional worldwide understanding of how a project is built and
categorized by specialty.
- Projects chosen offer little complexity
that would impact construction means and methods. The projects provide materials used in
nearly all construction projects such as concrete, steel, wood, and
plumbing piping, irrespective of what country or location this project may
be located.
- Projects chosen are easy to understand
allowing the estimator to grasp the overall project massing and
configuration. Workbooks contain
outline drawings.
- Project content provides for the basic
construction products used extensively in any project. This limits the specification issues
that provide inconsistency among different Countries. Basic materials such as concrete are
relatively similar from Country to Country.
- Designs chosen offer little complexity
for pricing purposes. If the
material or component is not widely used then an opportunity exists for
each individual estimator to customize pricing based upon best local
practices. This will occur to some
limited extent from Country to Country but as long as a substitute of
equal is priced then this variable factor will be minimized.
- Project site work and substructures are
quantified therefore minimizing project cost variances by building on a
flat site as compared to a steeply sloping site.
- Outline specifications provided show
basic specifications that allow the estimator to use more locally
compliant products.
It’s
accepted that the workbook could and should only be completed by someone
experienced in estimating construction projects. To have the workbook completed by
inexperienced estimators would only add to the potential for erroneous
data. By keeping the models and format
basic by design the chances of greater overall success will exist. A person experienced in estimating
construction costs should have little problem working through the workbook and
creating a complete price for each project.
The
probability of success with the collection of cost data must be viewed in two
parts. Part one being the design and
format of the actual workbook and part two being the expertise of the person
completing the workbook exercise. It
would be rather foolish to issue the workbook to an individual unqualified in
pricing BOQ or creating cost estimates.
The success of the workbook format will only exist if the data is priced
by qualified individuals. Even with
qualified individuals variations will occur.
Sinclair 3 found that even qualified estimators would not
produce equal estimates given the same information from which to create an
estimate. The balance of this paper
identifies this “estimating” problem to allow the perceived problems of
collecting data via workbooks to be put totally into perspective. The author of this paper agrues that
perfection of data collection can only be a goal but can never be achieved.
The
Estimating Problem
How does an estimator estimate the cost of a
construction project? For those reader’s
not familiar with cost estimating, the process involved is complex. Learning about cost estimating will help
non-cost-estimators understand what is involved and what limitations exist when
reviewing cost data generated by cost estimators.
Fig. 1.1 The estimating objective: to hit the target.
Figure 1.1 illustrates subjective
estimates attempting to hit the target, which is the actual cost. The subjective value chosen by each estimator
was considered to represent the resources required by each firm to complete an
example office-building project. We can
see that the estimates are all scattered around the target of actual cost. Hitting the target is not a common occurrence
and is an inbuilt problem of estimating.
Briefly,
let us consider an estimator pricing a brickwork item.
What are the difficulties
presented? They are as follows:
1.
Choice of work method.
2.
Output of crew (given the firm’s unique efficiency).
3.
Cost of labor
4.
Cost of material and selection of an appropriate wastage allowance.
5.
Addition of overheads and profit
Problem 1 - Choice of work Method
There may be many or only a few work
methods available. For instance, should
the estimator assume a three-man or a four-man crew, composed of two or three
bricklayer with either one or two laborers?
Will there be central mortar mixing or individual mixers for each crew? How will the brickwork be constructed? Will trestles or proper standing scaffolding
be used? Where will work commence from? What restrictions will the other trades
impose on the masonry work?
All possibilities must be investigated,
and the most economical possibility should be chosen.
Problem 2- Output of crew
The output chosen will be based on past
performance, since the estimator will assume that this performance will be
repeated in the future. As will be
explained later, recording and properly documenting job site performance is
helpful to the estimator when he or she considers future projects. Manipulation of these historical data may
occur; for example, decreasing output to allow for restricted working
condition. Whatever manipulation occurs,
the estimator is faced with the difficulty of trying to assess what output will
be achieved.
Problem 3- Cost of labor
How much will the contractor be
required to pay for labor? The estimator
must predict this cost. The labor cost
will vary depending on job location, availability of skilled labor, contract
wage regulations, union or open shop labor requirements, general market
conditions, and so on.
Problem 4- Cost of Material
This can be predicted with a fair
degree of accuracy if the material in question is in ready supply and is
frequently purchased. The quantity of
material required must be accurately measured from the drawing and is not
dependent on the crew performance or work method adopted. Although the estimator must not only
consider the finished in -place quantity of material, but also must allow for a
wastage factor, this factor can vary dramatically and is highly dependent on
the performance and work procedures adopted by the crew.
Problem 5 - Addition for overheads and profit
This amount will depend on company
policy, market condition, and many other variables that will be discussed
later. It is, as you can imagine, very
important to incorporate overhead and profit into the final estimate.
Problems 1-5 have been presented
simply, but you can begin to imagine their complexity.
An estimator has to posses the skill
and expertise to assemble the known facts and rationally solve the estimating
equation. How this is done is best
explained by reference to the decision tree diagram shown in figure 1.2.
Fig. 1.2 Hypothetical decision tree
diagram.
Figure 1.3 amplifies stages 5 and 6,
here the estimator selects a range of most likely values and, after a process
of fine tuning and “weighing up” of the situation, the estimator modifies his
or her initial crude selection and finally selects a value that he or she
considers to be ‘most likely.”
Fig. 1.3
Fine tuning an estimate.
The thought process previously described and shown in
fig.1.2 and 1.3 applies to our hypothetical brickwork example, but generally
indicates how and estimator arrives at a solution for each separate item of the
cost estimate. A total cost estimate
consists of numerous line items and specific sections relating to various
trades and specialists subcontractors.
This thought process will usually be repeated on numerous occasions
during the compilation of one single estimate or bills of quantity.
Location
Since a construction project’s location
affects the final cost, an estimator must understand what particular locational
factors will be encountered and what considerations should be taken into
account when formulating the estimate.
Estimators are aware that costs in Boston
are different that costs in Miami , but not
everyone is aware that the locational variation within the Boston
area or within the Miami
Various locational difficulties are
described:
1.
Remoteness
2.
Confined sites
3.
Labor availability
4.
Weather
5.
Design considerations (related to location).
6.
Vandalism and site security
Remoteness
A remote construction site, for
example, a project site located high in the Blue Ridge Mountains of Virginia
Communication Problems
If adequate communications such as
telephone are not available, then a radio or cellular-type installation is
required. A telephone is a requisite to
any construction project: lack of communication during the construction process
can result in major, costly errors. In
addition, because the project location is further away from the head office,
additional long-distance telephone charges will be incurred.
Transportation Problems
All material and labor must be
transported to the building site. If the
transport route is poor (if, indeed, any route exists at all), then delays in
material deliveries may occur; large vehicles may damage narrow bridges or
other items of property, whose replacements costs must be borne by the
contractor.
It may be necessary for the contractor
to widen the existing route or construct a bridge to allow material trailers
access into the job site. The route that
is proposed should be studied carefully by the estimator. Existing capacity of existing bridges on
route should be established to verify if equipment loads can be accommodated of
if the bridge needs to be strengthened by the contractor. Finally, the cost of hauling items of
equipment to the job site increases as the distance increases. Given these considerations, the requirement for
management to make the correct equipment selections becomes very important.
Increased Material Cost
Increased material cost is primarily
due to increased transport charges such as when distance for haulage from the
depot to a remote job site is longer than the haulage associated with other
construction projects the estimator has previously worked on. Avery4 found that if the material
was fragile or hazardous, then transport costs fluctuated widely depending on
distance. He also discovered that the
bulk materials with low initial cost, such as sand and gravel, tend to be the
most adversely affected by distance and difficult transport conditions. Ferry crossing or bridges with tolls increase
the basic cost of materials.
Power and Water
Power and water are a necessity for
building construction. Water is needed
for materials such as concrete, for cleaning the building, and for many other
uses. Salt water is not acceptable in
most specifications for concrete or mortar mixing, so remote projects without a
convenient domestic water supply, even if the site has access to thousands of
gallon of seawater; require water to be trucked to the job site. The cost of water depends on the hauling
costs. In some instances wells can be
dug to pump water to the surface; of course, the costs involved must be
considered in the estimate.
If no power source is available, then
power must be provided by generators.
Confined Sites
The problems associated with confined
sites generally take the form of congestion resulting in restricted working
areas resulting in low productivity from labor and equipment. These difficulties are generally associated
with downtown sites, but this need not always be the case.
In extreme cases, congestion can limit
the choice of work methods, types of equipment used, and size of crew to be
employed. Careful investigation of the
problems likely to be associated with each particular site will allow a
realistic assessment of factors such as productivity to be made. Project startup requires a careful
utilization of resources in order to provide production outputs that maximize
profits. Confined sites create
logistical problems. Material movement
should be minimized: each time an item of material is moved, its cost to
install in place increases. When
materials are delivered to a confined site, the material should be used immediately. If this is not possible, a storage area
should be available to receive the material, or, if possible, the material
should be offloaded directly at its intended utilization point.
The estimator needs to consider the
unique logistical problems associated with each job site. These problems, including restricted access,
restricted material lay down area, restricted equipment storage areas, and
restricted location for site trailers, affect the type of equipment that can be
used, the effective management of the job, the worker productivity, and the
amount of labor involved in handling material.
Since confined sites nearly always pose logistical problems, the unit
prices used by the estimator must account for the increased costs.
Labor Availability
Each location has varying amount
of available skilled and unskilled labor, depending on the condition of the
local economy. If labor of any kind is
not available locally (as may be the case in remote areas), then labor must be
imported from other location. In order
to move labor from one area to another, a financial incentive is usually
required. The magnitude of this
incentive will vary depending on the state of the labor market. If labor is imported, accommodations may have
to be provided. Labor camps comprising
full time kitchen staff, dormitories, leisure facilities, etc., have been set
up on major construction project to house the contractor’s labor force. The leisure facilities keep the labor force
relaxed and occupied during any rest periods.
Living and working on a remote construction site can be very
demoralizing, after a while, and by keeping the morale level high, labor
turnover is reduced. Generally, the cost
of importing labor will follow the laws of supply and demand.
Weather
Since
the building process is highly weather dependent, extreme conditions can
greatly affect building costs. These
extreme weather conditions include large amount of rain or snow, occurrences of
ice and frost, and high humidity and heat.
Their effects on cost include the following situation. Concrete pours in temperatures below 40
degrees Fahrenheit require special precaution.
With cold weather concreting, the cost of admixtures, insulation the
formwork, removing ice from formwork, and protecting the freshly placed
concrete from dropping below the specified temperatures must be taken in to
account by the estimator. Not only does
cold weather affect concrete, but hot weather concreting has its associated
problems as well. During periods when
the temperature exceeds 80 degrees Fahrenheit, special precautions are required
to reduce and maintain the concrete below this temperature. For example, ingredients such as the water
may be cooled or chopped ice can be utilized.
Another alternative is to use liquid nitrogen to cool the concrete. Admixtures and low heat cement can be used to
control the set and hardening times of the concrete to achieve the design
strength and quality. All these precautions
and procedures increase the cost of pouring, placing, and curing concrete.
Exposed
sites may have problems associated with high winds, which affect crane and
hoisting operations, and the contractor’s dust control program. Additional temporary bracing to partly
completed structures may be required to prevent a collapse due to high wind
gusts. In areas where hurricanes occur,
the estimator should consider the cost of temporary measures required to
prevent damage to a structure before, during, and after a hurricane. It would be prudent to allow for the costs
involved in bracing, tieing down structures providing sand banks, garaging
equipment, and storing particular materials such as doors and windows off the
job site, unless safe, dry, and secure storage exists on the project.
Labor
productivity is also associated with the weather. During poor weather when it is cold, damp,
and windy, the morale of workers exposed to adverse elements, drops, which in
turn results in a decline of productivity.
During days when it may be impossible to work, such as during a
torrential rain, the productivity is zero.
Design
Considerations (related to location)
The
location of a project has certain aspects that must be considered by a
designer. For example, in historic Frederick , Maryland
These
design considerations can create estimating problems in historic
districts. The estimator must know if
the materials specified are, in fact, locally available of if local labor
exists to carry out complicated historical work, such as ornate plaster work;
if not, a specialist will be required.
Traditional building techniques tended to be labor intensive. If the same techniques must be repeated, then
the estimator must be familiar with the procedures involved. If workers are
required to use traditional, building methods with which they are unfamiliar,
then a learning curve cost needs to be built into any unit price.
The
local climate also dictates the designer’s choices in mechanical and electrical
systems and in the choice of materials and design of the building
envelope. Material resources will
fluctuate from location to location throughout the country, and the designer
must investigate what materials are locally and economically available.
Finally,
each locality tends to have its own construction trade practices, and the
estimator should be familiar with them.
Vandalism
and Site Security
Site
integrity is an important problem in urban areas. Protective measures can be
expensive, for example, when 24-hour guard service and perimeter enclosures,
are required. The level of security will
depend on the risk to the project from the surrounding neighborhood. The local police should be consulted.
Variability of Estimates
The
following are where cost variances between one estimate and another can occur:
1.
Quantity take off.
2.
Material Costs.
3.
Labor Costs.
4.
Labor productivity forecasts.
5. Work
Methods.
6.
Construction equipment costs.
7.
Indirect Job costs.
8.
Subcontractor quotations.
9.
Quotations from material suppliers.
10. Unknown site conditions.
11. Locational Factors.
12. Cost associated with the time element of the
construction project and escalation
costs.
13. Staging and project start up costs.
14. Overheads.
15. Profit element.
16. Contingency and risk allocation.
17. Errors in estimate formulation.
18. Basis of information used to formulate
estimate.
19. Market forces.
Wendes5,
commenting on the estimating ability of estimators lists the following points
concerning their performance when estimating projects:
1. Reasonably correct with shop labor if
everything is standard.
2. Good with raw material and equipment pricing.
3. “Okay”
with subcontractor quotes if they are familiar with the work; “bomb out” if
they are unfamiliar.
4. At the “high school level” with their
quantity take offs.
5. Unsatisfactory with special items.
6. Poor with field labor.
7. Fail with overhead markups.
8. Coverage of profit is in the realm of wishful
thinking.
Variances
between estimates and actual costs do occur.
The estimator, unfortunately, always appears to be incorrect, since an
estimate is an “estimate”, which is a forecast of the anticipated future
cost. Many forces can, in reality, cause
the actual cost to vary from the estimated cost. It sometimes appears to owners and management
that, when the estimate does not equal the actual costs, a mistake has been
made. Because it is an estimate, it
should always be expected that the actual cost will vary somewhat from the
estimated cost. It is the job of the
estimator to minimize the extent of variance between estimate and actual
cost. Any data collection system must be
able to recognize that variances exist.
Explanation of Variances - Why Do
They Occur ?
As
previously discussed, the author believes that there are 19 major areas where
differences between cost estimates can exist.
When compiling the cost estimate, each of the 19 categories has to be
dealt with by the estimator. In dealing
with each category, the estimator has to make several assessments, such as what
subcontractor price for drywall should be used in the cost estimate or what
labor productivity shall be used for the carpenters installing intricate
millwork. The total cost estimate is
made up of numerous smaller cost estimates for each activity required to
complete the overall project. The
estimating equation is therefore composed of a series of calculations, the
estimator has to assess and propose a monetary solution. The total cost estimate is the total of all
the minor monetary solutions.
Each
assessment the estimator performs is based on:
- Previously recorded data (historical
data)
- The estimators own past experience.
- Previous experience of others.
- Hunches.
The
final assessment is subjective. The
estimator will decide what productivity to allow, or what dollar allowance or
unit price to use. Even though the
estimator has consulted with subcontractors, suppliers, site superintendents,
project managers, and others, when compiling his or her estimate, it is the
estimator who will decide what value will be used in the estimate. This subjective act is the main reason why
estimates vary. If you give identical
drawings and specifications to 100 estimators, you will get 100 different cost
estimates.
Figure
1.4 indicates the factors influencing variance in an estimate.
Fig.
1.4 Basic reasons for variances being introduced into cost estimates – the
subjective assessment.
Historical Data
Historical Data is used frequently by estimators when compiling cost
estimates, with their attendant advantages and disadvantages. There are some rules to be followed, which
are extremely important:
- Always understand the source of the
historical data.
- Always understand what the historical
data represent
- Always understand what time period the
historical data reflect.
·
Always
understand fully how to update and project the historical data to the present
time.
- Always understand how to manipulate the
data to represent your particular project, since no
- Two projects are the same.
- Always be wary of working with
historical data that you are not familiar with.
Various
sources of historical data are available, such as published price books, cost
information publication services, trade journals, and, most important, cost
feedback from actual projects that the estimators firm has been involved with
and therefore most knowledgeable of.
Actual
cost feedback is the best information to use if it were recorded and documented
properly. The feedback cycle (see Fig
1.5) is of critical importance. In order
for estimating to be effective, feedback from the job site must occur. Actual costs should be compared with
estimated costs to inform the estimator of his or her performance during the
estimating phase. Unfortunately, the
feedback process is not carried out effectively within the industry. To quote the Business Round Table Report on
modern management systems7: “Even within companies, a feedback of
actual costs is not consistently used to review and adjust the basis for
estimating future projects.”
Fig.
1.5 Company cost feedback cycle.
Sound
estimates are produced from a combination of experience and recorded cost data
of similar work previously performed.
The cost data, if proper feedback procedures have been adopted, will
have been refined over time to reflect accurate costs for performing certain
operations. The estimator can use these
data to formulate estimates accurately for future work. If the data to formulate are incorrectly used
or formulated, then mistakes will undoubtedly occur.
Accuracy Versus Economy
Estimating
involves the assessment of probabilities and risks making complete accuracy
impossible. However within the limits of
achievable accuracy, it can be stated that the greater the accuracy, the higher
the cost of achieving that accuracy.
There is usually a point beyond which the cost in increasing and
estimate’s accuracy is greater than the benefit to be gained.
Figure
1.6 indicates the accuracy versus economy dilemma. As more of the estimator’s time and effort
are devoted to the preparation of the cost estimate, a point is reached where
obtaining the utmost accuracy is not economical. As we have discussed 100% accuracy is
impossible.
Fig. 1.6
Estimating time required for a $2,000,000 building (© R.S. Means, Inc., 100
Construction Plaza, Kingston ,
MA
Figure
1.7 indicates the general accuracy that is expected by employing varying
amounts of estimating manpower.
Fig.
1.7 Estimate accuracy versus costs of estimate.
The Pareto Distribution in
Estimates
The
estimator will price (or at least consider) each item he has discovered, such
as cubic quantity of concrete footings, walls or slabs. These items may be in the form of a detailed
quantity take off or some other form sufficiently detailed to enable confident
estimating to occur.
Each
of the items discovered by the estimator has a cost importance that varies in
magnitude. Some items are of more cost
importance than others, since they form a larger percentage of the total cost
than the minor items do. The Pareto[1]
effect is seen to occur, that is, a small proportion of the items account for a
very large proportion of the cost.
Investigation into the cost structure of items in Bills of Quantities by
Brown 8 has shown that, typically, 20% of the items priced contained
at least 80% of the total cost. (See Fig
1.8)
Fig. 1.8
Pareto principle applied to estimating.
(Reprinted from R. Brown, Investigating into the Feasibility of
Applying the Pareto Principle to SMM Bills of Quantities of Cost Planning, Project
Report, Loughborough University ,
UK
The
Pareto effect can be used to great advantage by applying strict control over
the major items; the chance of major errors and discrepancies occurring is
therefore reduced. Owing to the time
constraints involved with preparing a competitive bid, the Pareto effect should
be taken advantage of. Estimators should
be quick to recognize what the major items of cost importance are and devote
attention to these items. When faced
with abnormal conditions, the search for the critical items of cost may take
longer, but the Pareto principle should still apply. Both Dubner and McKenzie1 and
Stapel2 recognized this aspect with current BOQ methods. We have attempted to provide concise and
specific line items in the modified work book approach to accomplish major
resource savings at very little, if any, expense of quality.
It
has been noted that wide variances do occur between estimates. If 100 estimators prepared an estimate for
the same project using identical drawings and specifications, then 100
different estimates would be submitted.
Remarkably, though, the bottom line of the estimates would be within an
acceptable range of some +/- 10% of each other.
This is often the case when contractors submit bids for projects. The bids submitted by the majority of bidders
are quite often very close to each other.
Though, when examination of the bidders estimates occur, the cost
difference between each of the trades differ greatly (up to 25%) and when
examination of the cost to complete each activity within each of the trades
occurs, the cost differences between each bidders numbers can be as much as
50%. The degree of difference between
estimates will therefore differ depending on whether you are examining the
bottom lines, the trade amounts, or the cost of activities within each
trade. Greater variances within
estimates occur when uncertainty exists, such as in excavation work. Our workbook format excludes site work and
varying site related features thus eliminating an area of major uncertainty.
Conclusions
The modified workbook approach
attempts to simplify yet increase the quality of information received through
cost data collection methods. It’s agreed by both Stapel2 and Dubner
and McKenzie1 that the preferred tool is the Bills of Quantity
Method. Our workbook format is based
upon abbreviated Bills of Quantities that provide a consistent set of line
items that can be priced without difficulty by a local estimator qualified in
construction cost estimating. The line
items proposed can provide information on various levels such as:
- Cost per building type
- Cost of each trade
- Cost of individual line items such as
concrete footings
These
levels of information can be used to formulate “basket” of data that could be
analyzed even further. Merging of the
Basket of Goods Collection Method and the Bills of Quantity Method is possible
given the simplified format of the modified workbook approach.
References:
1 Dubner
and McKenzie, Australian Bureau of Statistics paper submitted to international
conference on ICP, World Bank, Washington ,
DC
2
Stapel Silke, Eurostat, Paper submitted
to international conference on ICP World Bank, Washington, DC (11-13 March
2002).
3
D. Neil Sinclair, Estimating for
Abnormal Conditions, Industrial Press, Inc., New York , New York
4
D.W. Avery, “Problems of Locality in
Construction Cost Forecasting and Control,” in Building Cost Techniques,
edited by P.F. Brandon, E.F.N. Spon Ltd., New
York , New York
5 H.C. Wendes, The Eight Facets of the Estimating Diamond,
Heating/Piping/Air Conditioning, October 1976, pp. 51-56.
7 The
Business Roundtable, Modern Management Systems, The Business
Roundtable, New York , New York
8 R.
Brown, Investigating into the Feasibility of Applying the Pareto Principle
to SMM Bills of Quantities and Cost of Planning, Project Report, Loughborough University , UK
[1] At the
end of the 19th century an Italian economist, Vilfredo Pareto,
developed a curve known as “Pareto’s Law of Distribution.”
