Cost analysis and estimating for engineering and management ch06

Cost Analysis and Estimatingfor Engineering and Management Chapter 6 Estimating Methods... Unit Method Identify a Cost Driver  Use Historical Data  Find “Cost per…”  Square ft., poun

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Cost Analysis and Estimating

for Engineering and Management

Chapter 6 Estimating Methods

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 Introduction

 “Non-Analytic” Estimating Methods

 Cost & Time Estimating Relationships

 Learning Curves

 Proportional Relationships

 Using Probability and Statistics

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General Estimating Methods

 More Quantitative (Solid Information)

 Used for Pricing

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Comparison Method

 Bracket Unknown with Known

 Known Cost of Similar Product/Project

 Find Cost for Upper Bound

 Cost for a Lower Bound Is Good, too

 c  a  a  b  b 

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Comparison Example

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Unit Method

 Identify a Cost Driver

 Use Historical Data

 Find “Cost per…”

 Square ft., pound, kW, hp, etc.

 Average Cost

 Dependent on Quality of Model

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Estimating Relationships

 Cost (CER) or Time (TER)

 Math Models or Graphs

 Function of One or More Independent Variables - Causality

 CERs are Considered Preliminary

 Best if Used Within Data Range

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Performance Time Data

 Extends Time Study Standards

 Standard Time Good Only for

Operation(s) Studied

 Not Suitable Directly for Estimating

 Use Algorithm to Develop Time Study Data into PTD

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PTD Algorithm

 Collect Data

 Classify Data into Common Groups

 Use Regression

 Separate into Constant and Variable

 Set Variable into Equation or Table

 Complete, Test, Publish, Implement

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 Many (12 or so) Studies

 Process and Arrange Data

 Regression Analysis

 Determine Variable Elements

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Variable Element Test 1

 Is the Element Variable?

 Establish a Limit - P 1 (%)

 Check at Extremes of Range (x)

 Use Computed y Values

 “Conditionally” Variable if: ^

%

^ min

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Variable Element Test 2

 Is the Variability of the Element

Significant to the Overall Cost?

 Establish Another Limit P 2 (%)

 Exceeds Both Test 1 & 2 = Variable

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Process the Data

 Collect and Add All Constant Elements

 Provide Equations or Tables for Each Variable Element

 Use Rules for Setting Table Divisions

 Include PF&D

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Estimating Database

Set Up 1.2 hr Constant 0.87 min Load 3 rd Part

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Using the TER Database

 Select Set-Up Time

 Get Constant Unit Time

 Determine Value of Independent x

 Get Time Value from Equation or Table

 If x Is Between Table Values

 Use Higher Value

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The Learning Theory

 Time/Cost Decreases by a Constant %

 Each Time the Quantity Doubles

 Finding the “Slope”

s

log log

2 log

Eq 6.7

Eq 6.8

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The Learning Curve

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Logarithmic Function

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 Cumulative Time for N units

 Average Time per Unit for N units

Eq 6.10 1

u N

T

N u

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More Learning Curve Notes

log log

j i

j

i

N N

T

T s





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c r

Q

Q C

c

I

I Q

Q C

c r

r

Q Q

C Q

C

Eq 6.14 Eq 6.15 Eq 6.16

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Other CERs

 Caution, Keep Scale within Factor of 5

 Variable and Fixed Components

 Multi-Variable

Eq 6.17

Eq 6.18

m KQ

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Factor Method

 Mostly for Major Projects

 Summary Model

 Uses Separate Factors

 Includes Cost Index

e f C f C

C



 I r

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Using Probability and Statistics

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Expected Value

 Elements of Uncertainty Assigned

Probabilities

 Certain Events (NO Other Possibilities)

 Mutually Exclusive Events

 Probabilities Indicate the Future

C

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 Most Likely Value

 Optimistic and Pessimistic Estimates

 Expected Cost and Variance

 

6

L C

6 var

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