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Enhancing Cost Realism through Risk-Driven Contracting: Designing Incentive Fees based on Probabilistic Cost Estimates Maj Sean Dorey* ( [email protected] ) Dr. Josef Oehmen ( [email protected] ) Dr. Ricardo Valerdi ( [email protected] ) * The views expressed in this presentation are those of the author and do not reflect the official policy or position of the US Government, Department of Defense, or US Air Force
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Maj Sean Dorey* ( doreysp@yahoo ) Dr. Josef Oehmen ( oehmen@mit )

Feb 12, 2016

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Enhancing Cost Realism through Risk-Driven Contracting: Designing Incentive Fees based on Probabilistic Cost Estimates. Maj Sean Dorey* ( [email protected] ) Dr. Josef Oehmen ( [email protected] ) Dr. Ricardo Valerdi ( [email protected] ). - PowerPoint PPT Presentation
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Page 1: Maj Sean Dorey* ( doreysp@yahoo ) Dr. Josef Oehmen ( oehmen@mit )

Enhancing Cost Realism through Risk-Driven Contracting:

Designing Incentive Fees based on Probabilistic Cost Estimates

Maj Sean Dorey* ([email protected])Dr. Josef Oehmen ([email protected])Dr. Ricardo Valerdi ([email protected])

* The views expressed in this presentation are those of the author and do not reflect the official policy or position of the US Government, Department of Defense, or US Air Force

Page 2: Maj Sean Dorey* ( doreysp@yahoo ) Dr. Josef Oehmen ( oehmen@mit )

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Consistent Carl Lucky LucyAverage 200 100Standard Deviation* 10 25

My team can depend on me bowling very close to

my average.

• If Carl bowls a 225 and Lucy bowls a 125, who did better?– Carl, since it’s less likely for him to beat his average by 25 pins

*Bowling handicaps are not calculated this way…most people do not think in the probability domain.

Context(Part 1)

When I bowl well, my team usually wins!

Page 3: Maj Sean Dorey* ( doreysp@yahoo ) Dr. Josef Oehmen ( oehmen@mit )

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Consistent Carl Rowdy RobAverage 200 200Standard Deviation* 10 15

My twin brother, Rob, is all show.

• If Carl and Rob both bowl a 210, who did better?– Carl, since it’s less likely for him to beat his average by 10 pins

Rewards should be based on statistical likelihood, not raw pin count

*Bowling handicaps are not calculated this way…most people do not think in the probability domain.

My twin brother, Carl, has no flair.

Context(Part 2)

Page 4: Maj Sean Dorey* ( doreysp@yahoo ) Dr. Josef Oehmen ( oehmen@mit )

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Bottom Line Up Front

• With long-term production and sustainment contracts at stake, competition to win system development contracts is intense– Fixed-price contracts are inappropriate due to their potential for huge

losses– Cost-plus contracts are normally used, but inadvertently incentivize

overly optimistic cost proposals (since there is no chance to incur a loss)• Risk-driven contracts designed in the probability domain offer a

structured method to hold contractors and the government accountable for cost estimates– Limit maximum contractor losses to not overly penalize their

engagement in risky system development efforts

Risk-driven contracts should reduce cost overruns during EMD when cost uncertainty is high

Page 5: Maj Sean Dorey* ( doreysp@yahoo ) Dr. Josef Oehmen ( oehmen@mit )

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Outline

• Motivation• Common Contract Types• Incentive Fee Design• Discussion• Summary

Page 6: Maj Sean Dorey* ( doreysp@yahoo ) Dr. Josef Oehmen ( oehmen@mit )

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Outline

• Motivation– Burning Platform– Cost Growth vs. Cost Overruns– Overemphasis on Technical Cost Drivers?– Optimism Bias– Economic Theory

• Common Contract Types• Incentive Fee Design• Discussion• Summary

Page 7: Maj Sean Dorey* ( doreysp@yahoo ) Dr. Josef Oehmen ( oehmen@mit )

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MotivationBurning Platform

• FY13 President’s Budget Request is $614B (including OCO)1

– $179B for acquisitions ($109B for procurement, $70B for RDT&E)

$296B unfunded liability greater than annual acquisitions budget

Table copied from GAO-09-663T, Defense Acquisitions: Charting a Course for Lasting Reform, 2009.

Page 8: Maj Sean Dorey* ( doreysp@yahoo ) Dr. Josef Oehmen ( oehmen@mit )

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MotivationCost Growth vs. Cost Overruns

• Cost growth implies increase to system lifecycle costs• Cost overrun implies exceeding the current contract target cost

– Overruns do not necessarily indicate excessive expenditures,2 but they are almost always counterproductive:

Overruns

Adjustments between programs

Reductions in requirements

Reductions in quantity

Schedule extensionsFunding instability3

Damaged public perception2

Perceived management failure4

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MotivationOveremphasis on Technical Cost Drivers?

• Cost estimation guides written by:– Army, Navy, Air Force, NASA, GAO, RAND, ISPA/SCEA, SSCAG

• Articles, conferences, and training opportunities from:– ISPA, SCEA, SSCAG, SCAF

• Textbook:– Garvey, P. R. (2000). Probability methods for cost uncertainty analysis: A

systems engineering perspective. New York, NY: Marcel Dekker.• Popular software tools:

– ACEIT, Crystal Ball, @RISK, PRICE, SEER, NAFCOM, COCOMO II, COSYSMO

International Society of Parametric Analysts (ISPA); Society of Cost Estimating and Analysis (SCEA);Space Systems Cost Analysis Group (SSCAG); Society of Cost Analysis and Forecasting (SCAF);Automated Cost Estimating Integrated Tools (ACEIT); System Evaluation and Estimation of Resources (SEER);NASA/Air Force Cost Model (NAFCOM); Constructive Cost Model (COCOMO);Constructive Systems Engineering Cost Model (COSYSMO)

In an unbiased world, subject matter experts applying these tools and best practices would produce more accurate and reliable cost estimates

Page 10: Maj Sean Dorey* ( doreysp@yahoo ) Dr. Josef Oehmen ( oehmen@mit )

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MotivationOptimism Bias

• Optimistic technical estimates– Elicitation techniques required to “calibrate” experts confronted with

uncertainty5

• Optimistic management estimates– Government:

To maintain the appearance of affordability for new and existing programs, cost estimates that fit within authorized budgets are at least tacitly encouraged by the Services3,6

US Congressmen sometimes support programs with poor business cases when the funding is allocated to their constituents

– Contractors: Underestimate competitive program costs when not exposed to the risk of a loss

“I can think of a lot of programs in the Boeing Company where, if the estimate had been realistic, you wouldn’t have had the program. And that is the truth.”7

W. M. Allen – President, Boeing – 1964

Page 11: Maj Sean Dorey* ( doreysp@yahoo ) Dr. Josef Oehmen ( oehmen@mit )

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MotivationEconomic Theory

• Moral Hazard: the propensity to act differently when insulated from the risk of a loss8

– Underestimate competitive cost-plus proposals– Carry excess organization slack (operating and investment expenses)6

• Adverse Selection: government has imperfect knowledge of the expected costs of each contractor8

– Contractors have superior knowledge of underlying cost factors6

Direct access to the technicians and engineers who will be working on the contract

Close relationships with key suppliers Locally calibrated parametric cost models

Overcoming the issues associated with moral hazard and adverse selection requires risk sharing of overruns8

Page 12: Maj Sean Dorey* ( doreysp@yahoo ) Dr. Josef Oehmen ( oehmen@mit )

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MotivationEconomic Theory

• Contractors still benefit when they receive no profit9

– Scientists and engineers are gainfully employed (or hired) and available for future programs

– Technology competency is accrued, which improves their market position for future government and commercial business

– Facilities and equipment are often maintained and upgraded at the government’s expense

– Overhead expenses for other programs (and potential new programs) are slightly reduced by contributions to the overhead pool

Page 13: Maj Sean Dorey* ( doreysp@yahoo ) Dr. Josef Oehmen ( oehmen@mit )

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Outline

• Motivation• Common Contract Types

– Cost Plus Fixed Fee (CPFF)– Cost Plus Incentive Fee (CPIF)– Fixed Price Incentive Firm Target (FPIF)– Firm Fixed Price (FFP)– Usage by Acquisition Lifecycle Phase– Current Policy

• Incentive Fee Design• Discussion• Summary

Page 14: Maj Sean Dorey* ( doreysp@yahoo ) Dr. Josef Oehmen ( oehmen@mit )

Fixed Fee 100/0Share Line*

0

Profit

Cost

Target Cost

*100 = government’s share, 0 = contractor’s share

Min Fee

Max Fee

x/100-x Share Line*

0

Target Fee

Target Cost

Green = more profitOrange = less profit

Profit

Cost

*x = government’s share, 100-x = contractor’s share**RIE = Range of Incentive Effectiveness

RIE**

Max CostMin Cost

x/100-x Share Line*

*x = government’s share, 100-x = contractor’s share**PTA = Point of Total Assumption: point above which contractor assumes all costs

0

Profit

Cost

Target Profit

Target Cost

Green = more profitOrange = less profitRed = loss

PTA**0/100

Share Line

Ceiling Price

0

Profit

Cost

Target Profit

Target Cost

Green = more profitOrange = less profitRed = loss

0/100 Share Line*

*0 = government’s share, 100 = contractor’s share

FPIF

FFP

CPFF

CPIF

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Common Contract TypesUsage by Acquisition Lifecycle Phase

New risk-driven contract framework is targeted at EMD phase, but might also be appropriate during Tech Development or LRIP

Figure adapted from DoD Instruction 5000.02, 2008, p. 12.

CPFF/CPAF/CPIF Risk-Driven Contract FPIF FFP

Government assumes more cost risk

Contractor assumes more cost risk

More uncertainty Less uncertainty

Page 16: Maj Sean Dorey* ( doreysp@yahoo ) Dr. Josef Oehmen ( oehmen@mit )

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Common Contract TypesCurrent Policy

• USD(AT&L) recently set FPIF contract with 50/50 share line and 120% ceiling as the point of departure10

– Normally appropriate for early production– Compromise between CPAF and FFP– One size does not fit all

Policy does not directly address system development phase when cost uncertainty is even higher

Page 17: Maj Sean Dorey* ( doreysp@yahoo ) Dr. Josef Oehmen ( oehmen@mit )

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Outline

• Motivation• Common Contract Types• Incentive Fee Design

– Notional Cost Estimates– FPIF Method– Risk-Driven Method

• Discussion• Summary

Page 18: Maj Sean Dorey* ( doreysp@yahoo ) Dr. Josef Oehmen ( oehmen@mit )

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0 50 100 150 200 250 3000

0.002

0.004

0.006

0.008

0.01

0.012

0.014

0.016

0.018

0.02

Cost ($M)

Pro

babi

lity

blue mean = 100 ($M), blue variance = 500 ($M)2

red mean = 100 ($M), red variance = 2500 ($M)2

BlueRed

Expected cost = $100Mfor both blue and red

• Lognormal cost estimates for two different programs with same expected cost, but different uncertainties:– Blue (lower risk effort…LRIP)

Mean = $100M Variance = 500 ($M)2

Standard Deviation = $22.4M Coefficient of Variation = 0.22

– Red (higher risk effort…EMD) Mean = $100M Variance = 2500 ($M)2

Standard Deviation = $50M Coefficient of Variation = 0.50

Incentive Fee DesignNotional Cost Estimates (PDFs)

The red program has a greater chance of overrunning and underrunning Where there’s risk, there’s opportunity!

Page 19: Maj Sean Dorey* ( doreysp@yahoo ) Dr. Josef Oehmen ( oehmen@mit )

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Each point on the CDFs represents the confidence level for an equal or lesser cost. For example, there’s a 80%

confidence the red program will be $133.1M or less

Incentive Fee DesignNotional Cost Estimates (CDFs)

Cost ($M)

Confidence

Blue Red

65.0 25%

84.1 25%

89.4 50%

97.6 50%

100 54.4% 59.3%

117.5 80%

120 82.5% 73.3%

133.1 80%

140.3 95%

163.1 99%

194.5 95%

268.4 99%

0 50 100 150 200 250 3000

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Cost ($M)

Cum

ulat

ive

Pro

babi

lity

blue mean = 100 ($M), blue variance = 500 ($M)2

red mean = 100 ($M), red variance = 2500 ($M)2

BlueRed

$133.1M

80% Confidence

Level

Page 20: Maj Sean Dorey* ( doreysp@yahoo ) Dr. Josef Oehmen ( oehmen@mit )

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Profi

t

Profi

t

Cum

Pro

babi

lity

Incentive Fee Design

Risk-Driven MethodFPIF Method Cost

Cost

Cost CDFs

Magenta used when value applies to both blue and red programs

Risk-driven contract profit determined in the probability domain

Cum Prob Achieved0 0

0

Green = more profitOrange = less profitRed = loss

Page 21: Maj Sean Dorey* ( doreysp@yahoo ) Dr. Josef Oehmen ( oehmen@mit )

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• Expected profit determined by multiplying the profit at each cost by its corresponding probability and then summing all possibilities– Blue expected profit = $10.9M– Red expected profit = $7.5M

Expected profits are different for blue and red programsConfirms one size does not fit all

50 100 150 200 250

-50

-40

-30

-20

-10

0

10

20

30

40

50

Cost ($M)

Pro

fit (

$M)

Target Cost = $100M, Target Profit = $12M50/50 Sharing Ratio, 120% Ceiling

0

0.004

0.008

0.012

0.016

0.02

Pro

babi

lity

BlueRed

$100M TargetCost

$116M PTACost

$4M PTA

Profit

$12M TargetProfit

Incentive Fee DesignFPIF Method

Cost Domain

Page 22: Maj Sean Dorey* ( doreysp@yahoo ) Dr. Josef Oehmen ( oehmen@mit )

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0 0.2 0.4 0.6 0.8 1

-50

-40

-30

-20

-10

0

10

20

30

40

50

Cumulative Probability Achieved

Pro

fit (

$M)

BlueRed

Bluemean

(54.4%) Red mean

(59.3%)

$12M Target Profit

• Same contract, but x-axis changed to show profit earned as a function of cumulative probability achieved– For example, achieving the mean cost

($100M) on red program (p59.3) earns $12M

• Blue– Expected profit = $10.9M– Max loss = $43.1M

Cost (p99) – Cost (p82.5) = 43.1

• Red– Expected profit = $7.5M– Max loss = $148.4M

Cost (p99) – Cost (p73.3) = 148.4

Incentive Fee DesignFPIF Method

Probability Domain

This contract type clearly favors the blue cost estimate since the red max loss is not proportional to its expected profit4,11

Page 23: Maj Sean Dorey* ( doreysp@yahoo ) Dr. Josef Oehmen ( oehmen@mit )

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• Structured method to impose potential loss on contractors

• Blue & Red– Expected profit = $9.5M– Max loss (@ p99) = $25.3M

• Contractor earns equal profit for equivalent cost savings effort– For example, reducing cost from 50%

to 45% confidence level earns same profit increase for blue and red programs

Now expected profits and max losses all matchDetermining profits in probability domain normalizes cost estimate variances

Universal point of departure for system development programs?

Incentive Fee DesignRisk-Driven Method

Probability Domain

0 0.2 0.4 0.6 0.8 1-30

-20

-10

0

10

20

30

Cumulative Probability Achieved

Pro

fit (

$M)

Profit (p25) = $20M, Profit (p50) = $12MProfit (p80) = $0M, Profit (p95) = -$20M

$12M Target Profit

Blue & Redp50

$25.3MMax Loss

Blue & Redp99

Page 24: Maj Sean Dorey* ( doreysp@yahoo ) Dr. Josef Oehmen ( oehmen@mit )

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0 50 100 150 200 250 300-30

-20

-10

0

10

20

30

Cost ($M)

Pro

fit (

$M)

BlueRed

$89.4M (Red p50)

$97.6M(Blue p50)

$12MTarget Profit

• Same contract, but x-axis changed to show profit earned as a function of incurred cost

• Government shares larger portion of red profit below target cost in return for limiting contractor’s potential losses

Sharing curve flattens as cost uncertainty increasesAppropriate for government to share more risk for requiring more innovation

Incentive Fee Design Risk-Driven Method

Cost Domain

Page 25: Maj Sean Dorey* ( doreysp@yahoo ) Dr. Josef Oehmen ( oehmen@mit )

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Outline

• Motivation• Common Contract Types• Incentive Fee Design• Discussion

– Benefits– Drawbacks– Limitations

• Summary

Page 26: Maj Sean Dorey* ( doreysp@yahoo ) Dr. Josef Oehmen ( oehmen@mit )

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DiscussionBenefits

• Probabilistic cost proposals will give government more insight into contractor risk assessments

• More realistic cost estimates should lead to more predictable acquisition outcomes– Knowledge-based system development affordability assessments– If programs are still started, better chance they will be adequately

funded• Fewer cost overruns means less:

– Funding instability– Cancelled programs (and lost investments)– Management casualties

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• Government may have to allocate more funding to system development programs than usual (to cover wider range of possible costs)– Extra funding could be considered the usual cost of overruns– If required, could choose to terminate contract at p95 (or a little less);

just make sure to keep significant loss potential Reduces government’s share from $243.1M to $174.5M Reduces contractor’s potential loss from $25.3M to $20.0M

DiscussionDrawbacks

Page 28: Maj Sean Dorey* ( doreysp@yahoo ) Dr. Josef Oehmen ( oehmen@mit )

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• Risk-driven contracts do not directly address contract changes– However, with increased exposure to losses, contractors will likely:

Demand more clearly defined requirements and responsibly limit requirements creep

Augment precontract planning tasks Propose more mature technologies Recommend incremental or spiral development strategies

• If a change is necessary:– Consider applying the change to a separate CLIN (to maintain the

integrity of the base contract incentive structure)– Consider using the same probabilistic sharing ratios as base contract

(this could be prenegotiated)

DiscussionLimitations

Page 29: Maj Sean Dorey* ( doreysp@yahoo ) Dr. Josef Oehmen ( oehmen@mit )

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Outline

• Motivation• Common Contract Types• Incentive Fee Design• Discussion• Summary

Page 30: Maj Sean Dorey* ( doreysp@yahoo ) Dr. Josef Oehmen ( oehmen@mit )

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Summary

• Risk-driven contracts offer an alternative to traditional cost-plus contracts used for system development– Directly map probabilistic cost estimates to profit distributions– Offer structured method to impose chance of loss on contractors– Appropriately limit maximum losses for risky development efforts

• By properly aligning incentives with risk, risk-driven contracts should result in more realistic cost estimates– Reduces motivation for contractors to underbid competitions or

acquiesce to government pressure to fit within expected budgets without trimming requirements

• Net outcome should be fewer overruns and greater acquisition predictability

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References1. Department of Defense. (2012). Fiscal year 2013 budget request overview. Washington, DC: Office of the

Undersecretary of Defense (Comptroller).2. Cummins, J. M. (1977). Incentive contracting for national defense: A problem of optimal risk sharing. The Bell Journal

of Economics, 8(1), 168-185.3. Government Accountability Office. (2008). Defense acquisitions: A knowledge-based funding approach could improve

major weapons system program outcomes (GAO Report No. 08-619). Washington, DC: U.S. Government Printing Office.

4. Scherer, F. M. (1964). The theory of contractual incentives for cost reduction. The Quarterly Journal of Economics, 78(2), 257-280.

5. Hubbard, D. W. (2010). How to measure anything: Finding the value of “intangibles” in business (2nd ed.). Hoboken, NJ: John Wiley & Sons.

6. Williamson, O. E. (1967). The economics of defense contracting: Incentives and performance. In R. N. McKean (Ed.), Issues in Defense Economics (pp. 217-256). National Bureau of Economic Research.

7. Butts, G., & Linton, K. (2009). NASA’s joint confidence level paradox: A history of denial. 2009 NASA Cost Symposium.8. McAfee, R. P., & McMillan, J. (1986). Bidding for contracts: A principal-agent analysis. The RAND Journal of Economics,

17(3), 326-338.9. Fox, J. R. (1974). Arming America: How the U.S. buys weapons. Cambridge, MA: Harvard University Press.10.Carter, A. B. (2010). Better buying power: Guidance for obtaining greater efficiency and productivity in defense

spending [Memorandum]. Washington, DC: Office of the Under Secretary of Defense for Acquisition, Technology and Logistics.

11.Kahneman, D., & Tversky, A. (1984). Choices, values, and frames. American Psychologist, 39(4), 341-350.

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Backups

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VignettesWith Risk-Driven Contracts

• Purposely estimate low mean cost (to win competition and/or meet government affordability threshold)– Much higher chance of incurring substantial loss

• Purposely estimate high mean cost (to increase profit potential and reduce loss potential)– May lose competition and/or exceed government affordability threshold

• Purposely estimate large cost variance (to reduce loss potential)– Also reduces profit potential– May lose competition and/or exceed government affordability threshold– Government more likely to question cost realism

• Purposely estimate small cost variance (to increase profit potential)– Also increases loss potential– Government more likely to question cost realism

No easy way to game the system – Honesty is best policy!

Page 34: Maj Sean Dorey* ( doreysp@yahoo ) Dr. Josef Oehmen ( oehmen@mit )

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• Need to require probabilistic cost estimate as part of cost proposal– Risk-neutral program office should

select proposal with lowest expected cost (all other factors being equal)

– Risk-averse program office should also consider variance of each cost proposal (all other factors being equal)

Probabilistic Source Selection

50 100 150 2000

0.005

0.01

0.015

0.02

0.025

0.03

Cost ($M)

Pro

babi

lity

blue mean = 100 ($M), blue variance = 800 ($M)2

red mean = 110 ($M), red variance = 200 ($M)2

BlueRed

Page 35: Maj Sean Dorey* ( doreysp@yahoo ) Dr. Josef Oehmen ( oehmen@mit )

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Calculating Profit

• Example incentive fee payment for blue program:– Final cost = $95M– Recall: m = $100M, v = 500 ($M)2

– Calculate μ and σ using these equations: μ = 4.5808 σ = 0.2209

– Determine cumulative probability achieved using Microsoft Excel lognormdist (95, 4.5808, 0.2209) = 0.4515

– Recall: Profit (p25) = $20M, Profit (p50) = $12M– Interpolate to determine final profit: $13,550,761.52

• Consider using earned value estimate at completion (EAC) to calculate incremental incentive fee payments

22 /ln mvm

1/ln 2 mv

Note:ln() is the natural

logarithm function

4515.025.0

50.025.0122020

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Motivation2010 QDR

Our system of defining requirements and developing capability too often encourages reliance on overly optimistic cost estimates. In order for the Pentagon to produce weapons systems efficiently, it is critical to have budget stability—but it is impossible to attain such stability in DoD’s modernization budgets if we continue to underestimate the cost of such systems from the start. We must demand cost, schedule, and performance realism in our acquisition process, and hold industry and ourselves accountable. We must also ensure that only essential systems are procured, particularly in a resource-constrained environment. There are too many programs under way. We cannot afford everything we might desire; therefore, in the future, the Department must balance capability portfolios to better align with budget constraints and operational needs, based on priorities assigned to warfighter capabilities.

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Common Contract TypesCost Plus Award Fee (CPAF)

• Subjective, unilateral evaluation of contractor’s performance based on award fee plan criteria– Allows consideration of “conditions under

which [performance] was achieved” [FAR 16.401(e)(1)(ii)]

• “Suitable for use when the work to be performed is such that it is neither feasible nor effective to devise predetermined objective incentive targets applicable to cost, schedule, and technical performance” [FAR 16.401(e)(1)(i)]

• Periodic evaluations can lead to short-term optimizations

• Low ratings may cause tension• Little incentive to control requirements

creep since goal is to keep government happy

• Large administrative burden

Fixed Fee 0-3%

Award Fee Pool

Max Fee

Min Fee 100/0Share Line*

0

Profit

Cost

Green = more profit

Orange = less profit

Target Cost

*100 = government’s share, 0 = contractor’s share

Page 38: Maj Sean Dorey* ( doreysp@yahoo ) Dr. Josef Oehmen ( oehmen@mit )

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Probabilistic Cost Estimation

• Lognormal Distribution Review• Methods Overview• Parametric Cost Estimation• Engineering Buildup• Expert Opinion Elicitation

Page 39: Maj Sean Dorey* ( doreysp@yahoo ) Dr. Josef Oehmen ( oehmen@mit )

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Probabilistic Cost EstimationLognormal Distribution Review

0 50 100 150 2000

0.005

0.01

0.015

0.02

0.025mean = 50 ($M), variance = 500 ($M) 2

Cost ($M)

Pro

babi

lity

PDFmodemedianmean

Mode Median Mean

Cost $38.0M $45.6M $50.0M

Probability 0.0224 0.0205 0.0183

Probability Distribution Function (PDF)

0 50 100 150 2000

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1mean = 50 ($M), variance = 500 ($M) 2

Cost ($M)

Cum

ulat

ive

Pro

babi

lity

CDFmodemedianmean

Mode Median Mean

Cost $38.0M $45.6M $50.0M

Cumulative Probability 0.335 0.500 0.585

Cumulative Probability Distribution Function (CDF)

• Lognormal PDF is skewed to the right– Reflects disproportionate chance of an overrun11

• Mode = single most probable value, peak of PDF• Median = 50th percentile: 50% values lower, 50% values higher• Mean = expected value; average of all possible outcomes

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Probabilistic Cost EstimationMethods Overview

• Two basic methods to estimate cost uncertainty:12

– Parametric based on Cost Estimating Relationships (CERs)– Engineering Buildup based on Work Breakdown Structure (WBS)

elements– Not mutually exclusive; can be used together when appropriate

• Both require expert opinion elicitation for inputs• Both should be sanity checked against similar past projects

(analogy method)• Both should also consider the Scenario-Based Method (SBM) to

consider other possible risks13

• Both produce a PDF and CDF that quantifies the expected value and variance

Page 41: Maj Sean Dorey* ( doreysp@yahoo ) Dr. Josef Oehmen ( oehmen@mit )

41/31Figure copied from SSCAG Space Systems Cost Risk Handbook, 16 November 2005.

Probabilistic Cost EstimationParametric Cost Estimation

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Probabilistic Cost EstimationEngineering Buildup

2.4.1

WBS Element

2.4.2

2.4.3

2.4

Resultant PDF based on Monte Carlo draw from each WBS element PDFCare must be taken to properly handle correlation between elements

Page 43: Maj Sean Dorey* ( doreysp@yahoo ) Dr. Josef Oehmen ( oehmen@mit )

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Probabilistic Cost EstimationExpert Opinion Elicitation

0 2 4 6 8 10 120

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

Lines of Code [100K]

Pro

babi

lity

Triangular PDF

Most Likely

MaxMin

• Simplified example for software lines of code

• Experts asked to quantify min, max, and most likely estimates based on their experience

• Triangular PDF is easily generated• Extensive literature available on

best elicitation methods13

– Most likely estimate usually overly optimistic

– Max usually not worst case