Outcomes in Decision Analysis: Utilities, QALYs & DALYs, and Discounting DCEA 24 January 2013 James G. Kahn.
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Outcomes in Decision Outcomes in Decision Analysis: Utilities, Analysis: Utilities,
QALYs & DALYs, and QALYs & DALYs, and DiscountingDiscounting
DCEA24 January 2013
James G. Kahn
OverviewOverview
Back to the aneurysm example: Back to the aneurysm example: To Clip Or Not To Clip? To Clip Or Not To Clip?
Clinical OutcomesClinical Outcomes Utilities and utility measurementUtilities and utility measurement
Direct Direct IndirectIndirect
QALYs (& DALYs)QALYs (& DALYs) DiscountingDiscounting
Review—Last LectureReview—Last Lecture
• Formulated an explicit questionFormulated an explicit question
““to clip or not to clip” (incidental to clip or not to clip” (incidental aneurysm)aneurysm)
• Made a simple decision treeMade a simple decision tree• Conducted an expected value calculation to Conducted an expected value calculation to
determine which course of action would determine which course of action would likely yield the highest life expectancylikely yield the highest life expectancy
To Clip or Not To ClipTo Clip or Not To Clip
.865 vs .977
M s. B rooks
N o trea tm ent
S urgery
Surgery:yes or no?
AneurysmRupture?
Nop=0.9825 Norm al surviva l=1
Yesp=0.0175
Early Death=0
SurgicalDeath?
Nop=0.977
Yesp=0.023 Early Death=0
Death?
Nop=.55
Yesp=.45
Norm al surviva l=1
AneurysmRupture?
Nop=1.0 Norm al surviva l=1
Yesp=0
Early Death=0
Death?
Nop=.55
Yesp=.45
Norm al surviva l=1
=1.0
=.55
=.55
=.9921
=.977
Diff = -0.0151 =0
To Clip or not to Clip?To Clip or not to Clip? Has an impact on life expectancyHas an impact on life expectancy
Also actual clinical outcomes:Also actual clinical outcomes: Surgical deathSurgical death Aneurysm ruptureAneurysm rupture Death from aneurysm ruptureDeath from aneurysm rupture Neurologic InjuryNeurologic Injury
MajorMajor MinorMinor
Fear of aneurysm ruptureFear of aneurysm rupture
Quantifying Health OutcomesQuantifying Health Outcomes• Mortality • Life Years
number of expected years of life • Significant Morbidity
Paralysis, loss of sight• Quality Adjusted Life Years
Life years adjusted for value of health state• Disability Adjusted Life Years
Disease burden – lost years + disability• Financial Valuation of Outcomes
Costs to patient, payer, or society Willingness to pay to avoid outcomes
Health Outcomes – MortalityHealth Outcomes – Mortality• MortalityMortality
Death from disease/accident/procedureDeath from disease/accident/procedure
e.g. If Ms. Brooks undergoes surgery, one of the e.g. If Ms. Brooks undergoes surgery, one of the possible outcomes is mortalitypossible outcomes is mortality
• Life Years Life Years Calculate an expected value of life years using a Calculate an expected value of life years using a
probabilistically weighted average of expected life probabilistically weighted average of expected life
e.g. If Ms. Brooks does not undergo surgery, her life e.g. If Ms. Brooks does not undergo surgery, her life expectancy is less than if she did not have expectancy is less than if she did not have aneurysm, these outcomes are measured in aneurysm, these outcomes are measured in expected life yearsexpected life years
Health Outcomes – MorbidityHealth Outcomes – Morbidity
• MorbidityMorbiditySome health state that is less than perfectSome health state that is less than perfecte.g. disability from stroke, chronic paine.g. disability from stroke, chronic pain
• Comparison of morbiditiesComparison of morbidities Difficult – apples and oranges problem Difficult – apples and oranges problem e.g. which is worse:e.g. which is worse:Blind v. DeafBlind v. DeafDeaf v. ParaplegiaDeaf v. ParaplegiaParaplegia v. BlindParaplegia v. Blind
To Clip or not to Clip?To Clip or not to Clip? Clinical outcomes for clinician readersClinical outcomes for clinician readers
Outcomes may affect health-related Outcomes may affect health-related quality of life: quality of life: how do we compare?how do we compare?
Neurologic injury can cause Neurologic injury can cause mild/moderate disabilitymild/moderate disability
Not clipping can cause anxiety associated Not clipping can cause anxiety associated with being at risk of aneurysm rupturewith being at risk of aneurysm rupture
Outcomes may occur at different timesOutcomes may occur at different times
How do we incorporate quality-of-life How do we incorporate quality-of-life effects into decision analysis?effects into decision analysis?
Measure/estimate and apply Measure/estimate and apply health state health state utilitiesutilities
Use utilities to quality-adjust life expectancy Use utilities to quality-adjust life expectancy for decision and cost-effectiveness analysisfor decision and cost-effectiveness analysis
Preview—Where We Are Preview—Where We Are Going with this Analysis?Going with this Analysis?
Recall Ms. Brooks and her incidental aneurysm -- to Recall Ms. Brooks and her incidental aneurysm -- to clip or not to clip?clip or not to clip?
We want to: We want to: • Determine her utilities Determine her utilities • Use them to generate QALYs Use them to generate QALYs • Evaluate incremental QALYs and cost (CEA/CUA)Evaluate incremental QALYs and cost (CEA/CUA)• Compare incremental cost effectiveness ratios Compare incremental cost effectiveness ratios
(ICER) to other currently accepted medical (ICER) to other currently accepted medical interventionsinterventions
What is a Utility?What is a Utility?UtilityUtility - Quantitative measure of the strength of - Quantitative measure of the strength of an individual’s preference for a particular an individual’s preference for a particular health state or outcome. health state or outcome.
Utilities can be obtained for:Utilities can be obtained for:* * Disease statesDisease states (diabetes, depression) (diabetes, depression)* * Treatment effectsTreatment effects (cure, symptom (cure, symptom management)management)* * Side effectsSide effects (impotence, dry mouth) (impotence, dry mouth)* * ProcessProcess (undergoing surgery, prenatal (undergoing surgery, prenatal diagnostic procedure) diagnostic procedure)
UtilitiesUtilities
Utilities are the currency we use to assign values to outcomes
Scaled from 0 to 1
1 = perfect or ideal health or health in the absence of the condition being studied
0 = death
How are utilities measured?How are utilities measured?
• Direct Direct – compare with 0 / 1 anchors– compare with 0 / 1 anchors - Visual Analog Scale- Visual Analog Scale - Standard Gamble- Standard Gamble - Time Trade-off- Time Trade-off• IndirectIndirect Assess standard health domains (e.g., Assess standard health domains (e.g.,
physical functioning, pain, and cognition) physical functioning, pain, and cognition) and calculate 0-1 utility with an equation. and calculate 0-1 utility with an equation.
Direct utility Direct utility measurementmeasurement
BKA vs. AKA ExampleBKA vs. AKA ExamplePatient in hospital has infection of the leg Patient in hospital has infection of the leg
Two options: Two options:
1) 1) BKA – below knee amputationBKA – below knee amputation
BKA –1% mortality riskBKA –1% mortality risk
2)2) Medical management Medical management – 20% chance of – 20% chance of infection worsening and needing AKA (above infection worsening and needing AKA (above the knee amputation), 10% mortality riskthe knee amputation), 10% mortality risk
For which outcomes do we need For which outcomes do we need to measure utilities?to measure utilities?
Living without part of a leg (below the Living without part of a leg (below the knee)knee)
Living without a bigger part of a leg Living without a bigger part of a leg (above the knee)(above the knee)
PainPain WorryWorry OtherOther
Visual Analog ScaleVisual Analog Scale
100 98
2
0
99
65
55
1
Full health: intact leg
Dead
BKA
Outcomes rated on a 0-to-100 “feeling thermometer.”Outcomes rated on a 0-to-100 “feeling thermometer.”
AKA
Standard GambleStandard Gamble
What chance of immediate death would you What chance of immediate death would you be willing to incur to avoid living with the be willing to incur to avoid living with the outcome being assessed?outcome being assessed?
Method relies on respondents choosing Method relies on respondents choosing between:between:
1) a certain outcome (BKA)1) a certain outcome (BKA)
2) a gamble between an ideal outcome 2) a gamble between an ideal outcome (intact leg) and the worst outcome (dead)(intact leg) and the worst outcome (dead)
Standard Gamble QuestionStandard Gamble Question
Choose BKA?
Yes
No
BKA (intermediate outcome)
Perfect health
Death
Live?
p %
(100-p) %
Death
Perfect Health
Standard Gamble Exercisexercise
Spend the rest of your life with BKA
[p]]% chance of immediate deathimmediate death
1-[p]% chance of 1-[p]% chance of spending the rest of your spending the rest of your
life with an intact leglife with an intact leg
Which do you prefer?
Choice A Choice B
Standard GambleStandard Gamble
• Standard gamble measurement involves questioning patients to determine the p at which the two outcomes are equivalent
• Using expected utilities, the value of p implies the utility
Utility (BKA) x Prob (BKA) = Utility(cure) x (1-p) + Utility(death) x (p)
Thus, if utility of cure = 1 and of death = 0, the utility of BKA = 1-p.
Time TradeoffTime Tradeoff
How many years of your life would you be How many years of your life would you be willing to give up to spend your remaining willing to give up to spend your remaining life without the condition/health state being life without the condition/health state being assessed? assessed?
Method relies on respondents Method relies on respondents choosing between:choosing between:
1) Full life expectancy with the 1) Full life expectancy with the condition/outcome being assessed (BKA)condition/outcome being assessed (BKA)
2) A reduced life expectancy with the 2) A reduced life expectancy with the ideal outcome (intact leg)ideal outcome (intact leg)
Time Tradeoff Preference Elicitation
Spend the remaining 40 years of your life
with BKA
Live 40 more years of life with an intact leg (give
up 0 years of life)
Which do you prefer?
Choice A Choice B
Time Tradeoff Preference Elicitation
Spend the remaining 40 years of your life
with BKA
Live 30 more years of life with an intact leg (give
up 10 years of life)
Which do you prefer?
Choice A Choice B
Utility Measurement – Time Utility Measurement – Time Trade-offTrade-off
Find years of life at which patient is indifferent between Choice A (with health problem) & Choice B (shorter life).
We assume that: Time A * Utility A = Time B * Utility B
And thus Utility A = [Time B * Utility B] / Time A
If willing to give up 4 years to avoid BKA: Utility of BKA = [(40-4) * 1] / 40 = 36/40 = 0.9
Pros and Cons - VASPros and Cons - VAS
Advantage: Advantage: Easy to understandEasy to understand
Disadvantages: Disadvantages:
Doesn’t require the respondent to: Doesn’t require the respondent to:
- Think about what they’d be willing to give up- Think about what they’d be willing to give up
- Explore risk preference- Explore risk preference
Values spread over the rangeValues spread over the range
Pros and Cons – SGPros and Cons – SG
Advantages: Advantages: Requires assessor to give Requires assessor to give something up, incorporates risk attitudesomething up, incorporates risk attitude
Disadvantages: Disadvantages:
Choices may be difficult to make Choices may be difficult to make
Most confusion-prone methodMost confusion-prone method
Lack of engagement or willingness to participate Lack of engagement or willingness to participate in exercisein exercise
Utility values tend to cluster near 1Utility values tend to cluster near 1
Pros and Cons – TTOPros and Cons – TTOAdvantages: Still asking assessor to give something up Easier choices than SG. Values not so clustered near 1
Disadvantages: Fails to incorporate riskLack of clarity of when time traded occurs Isn’t something that one can choose to give up. (One can take on a risk of death, but not “pay with life years.”)
Indirect measures of utilityIndirect measures of utility First assess features of health using
standard domains (attributes) respondents complete a questionnaire
Then calculate utility (0 - 1) with equation score using a “multi-attribute scoring
function” derived from community preferences for health states defined by these attributes
http://www.healthutilities.com/hui3.htm
Source: Arnold 2009 BMJ
Utilities in decision Utilities in decision analysisanalysis
• Utilities are used to add Utilities are used to add morbiditymorbidity effects effects to life expectancy.to life expectancy.
• Quality Adjusted Life-Years (QALYs)Quality Adjusted Life-Years (QALYs) (we’ll return to DALYs later) (we’ll return to DALYs later)
QALYsQALYs• QALYs are usually considered the standard unit QALYs are usually considered the standard unit of comparison for outcomes for CEAs in OECDof comparison for outcomes for CEAs in OECD
• QALYs = time (years) x quality (utility)QALYs = time (years) x quality (utility)
• e.g. 40 years life expectancy after AKA, e.g. 40 years life expectancy after AKA, • utility (AKA) = 0.9utility (AKA) = 0.9 = 40 x 0.9 = 36 QALYs (undiscounted)= 40 x 0.9 = 36 QALYs (undiscounted)
•Mortality lowers LY, morbidity lowers QAMortality lowers LY, morbidity lowers QA
Back to aneurysmBack to aneurysm
M s. B rooks
No treatm ent
Surgery
Surgery:yes or no?
AneurysmR upture?
N op=0.9825 N orm al survival=1
Yesp=0.0175
Early Death=0
SurgicalDeath?
N op=0.977
Yesp=0.023 Early Death=0
Death?
N op=.55
Yesp=.45
N orm al survival=1
AneurysmR upture?
N op=1.0 N orm al survival=1
Yesp=0
Early Death=0
Death?
N op=.55
Yesp=.45
N orm al survival=1
Now we want to add utilities Now we want to add utilities for intermediate outcomesfor intermediate outcomes
Normal survivalNormal survival 1.01.0
Worry about possibility of Worry about possibility of aneurysm ruptureaneurysm rupture
0.950.95
Stroke utility (clipping compli-Stroke utility (clipping compli-cation or aneurysm rupture)cation or aneurysm rupture)
(0.76+.25)/2=0.5 (0.76+.25)/2=0.5
Survival adjmt due to strokeSurvival adjmt due to stroke 0.330.33
Immediate deathImmediate death 0.00.0
QALYsNo aneurysm rupture0.9825
No surgery34.86 Die
Aneurysm rupture 0.450.0175 Survive
0.55
No aneurysm ruptureDifference 1
_ QALYs -2.85 Survive surgery0.902 Die
Aneurysm rupture 0.45Clipping 0 Survive
32.01 0.55Key Inputs Surgery-induced disabilityRupture risk/yr 0.0005 0.075Expected life span 35RR rupture w/ surgery 0 Surgical deathSurgical mortality 0.023 0.023Surg morb (disability) 0.075
0.0
Ms. Brooks
17.5
35.0Normal survival
Disability, shorter survival
5.8
Immediate death
Normal survival 35.0
Normal survival
Normal survival
Early death
Early death
35.0
17.5
35.0
Including utility for early death Including utility for early death and disability due to strokeand disability due to stroke
Adding utility for worry =.95Adding utility for worry =.95(in No surgery arm)(in No surgery arm)
QALYsNo aneurysm rupture0.9825
No surgery34.78 Die
Aneurysm rupture 0.45
0.0175 Survive0.55
No aneurysm ruptureDifference 1
Δ QALYs -2.77 Survive surgery0.902 Die
Aneurysm rupture 0.45
Clipping 0 Survive32.01 0.55
Key Inputs Surgery-induced disabilityRupture risk/yr 0.0005 0.075
Expected life span 35RR rupture w/ surgery 0 Surgical deathSurgical mortality 0.023 0.023
Surg morb (disability) 0.075
Normal survival,worry
34.91
Normal survival
Normal survival
Early death,worry
Early death
35.0
17.5
35.0
0.0
Ms. Brooks
17.46
34.91Normal survival,
worry
Disability, shorter survival
5.8
Immediate death
Outcomes - DiscountingOutcomes - Discounting• Aneurysm ExampleAneurysm Example• We said since life expectancy is reduced by We said since life expectancy is reduced by 2/3, so instead of 35, it is = 35 * .333 = 11.672/3, so instead of 35, it is = 35 * .333 = 11.67
• However, However, are all years considered equalare all years considered equal??• Consider: Consider: Favorite MealFavorite Meal
Extreme PainExtreme Pain
Lifetime IncomeLifetime Income
Outcomes - DiscountingOutcomes - Discounting• Generally, present value more than futureGenerally, present value more than future• One way to value the different times is One way to value the different times is discounting discounting • Essentially this year is worth D more than Essentially this year is worth D more than next yearnext year• D (annual discount rate) usually set at 3%D (annual discount rate) usually set at 3%• To compare values of all future times, a To compare values of all future times, a calculation, net present value, is often usedcalculation, net present value, is often used• NPV = 1 / (1 + D)NPV = 1 / (1 + D)t t Where t is number of years Where t is number of years in the futurein the future
Outcomes - DiscountingOutcomes - Discounting• Aneurysm ExampleAneurysm Example• If utility is 0.6 and life expectancy is If utility is 0.6 and life expectancy is 3 years3 years• NPV would be: NPV would be: Utility / (1 + D) Utility / (1 + D)tt or or
NPV = 0.6 / 1 + 0.6 / (1.03)NPV = 0.6 / 1 + 0.6 / (1.03)11 + 0.6 / + 0.6 / (1.03)(1.03)22
• However, since events in year 1 occur However, since events in year 1 occur on average half way through, we can on average half way through, we can use 0.5 for year 1:use 0.5 for year 1:
NPV = 0.6 / (1.03)NPV = 0.6 / (1.03)0.50.5 + 0.6 / (1.03) + 0.6 / (1.03)1.51.5 + + 0.6 / (1.03)0.6 / (1.03)2.52.5
Outcomes - DiscountingOutcomes - DiscountingQALYs
discNo aneurysm rupture0.9825
No surgery21.37 Die
Aneurysm rupture 0.450.0175 Survive
0.55
No aneurysm ruptureDifference 1
Δ QALYs -1.63 Survive surg.0.902 Die
Aneurysm rupture 0.45Clipping 0 Survive
19.74 0.55Key Inputs Surgery-induced disabilityRupture risk/yr 0.0005 0.075Expected life span 35RR rupture w/ surgery 0 Surgical deathSurgical mortality 0.023 0.023Surg morb (disability) 0.075
Normal survival,worry
21.4
Normal survival
Normal survival
Early death,worry
Early death
21.5
Ms. Brooks
13.3
21.4Normal survival,
worry
0.0
Disability, shorter survival
13.4
21.5
4.8
Immediate death
QALYs vs. DALYsQALYs vs. DALYs “Quality Adjusted Life Years” (QALYs)
came first; still used for CEAs in OECD measure of health. An illness which shortens life by 2 years and lowers
“health status utility” by 20% for 5 years decreases QALYs by -2 - 0.2 * 5 = -3
Interventions are designed to increase QALYs
“Disability Adjust Life Years” (DALYs) most common health metric in global health. measure of disease burden – i.e., the negative of QALYs. An illness which shortens life by 2 years and raises
“disability” by 20% for 5 years increases DALYs by 2 + 0.2 * 5 = 3
Interventions are supposed to avert DALYs.
Geographic setting
Measures Components Goal is to:
Quality-Adjusted Life Years (QALYs)
U.S., Europe, and other OECD
countries
Health status
“LY” is gain in life years due to intervention.
“QA” is gain in health status utility* due to better health.
Gain
Disability-Adjusted Life Years (DALYs)
Global, and developing
world
Disease burden
“LY” is life years lost due to premature death.
“DA” is disability* due to morbidity.
Avert
* In practice, methods to estimate disability weight and health status utility often overlap, relying on similar elicitation of expert or patient or population opinion.
Excel workbook
Exponential DiscountingExponential Discounting
Exponential discounting first described in 1937* Mathematically easy to manipulate
Assumed discounting in “simple regular fashion”
Does not differentiate difference between: Today vs. tomorrow Ten years vs. ten years plus one day
*Samuelson PA. A Note on Measurement of Utility. Rev Econ Stud 1937;4:155-61
Overall ReviewOverall Review• Outcomes - ClinicalOutcomes - Clinical
Mortality - timingMortality - timing
Morbidity – severity, duration, timingMorbidity – severity, duration, timing
• Measuring UtilitiesMeasuring UtilitiesDirect – TTO most oftenDirect – TTO most often
Indirect – may underestimate utilityIndirect – may underestimate utility
• QALYs - health, DALYs – disease burdenQALYs - health, DALYs – disease burden• Discounting Discounting
NPV = NPV = Utility / (1 + D) Utility / (1 + D)t t
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