Decision AnalysisDecision Analysis

What is decision analysis?What is decision analysis?

Based on expected utility theoryBased on expected utility theory Used in conditions of uncertaintyUsed in conditions of uncertainty Decision process logical and rationalDecision process logical and rational Works on basis that rational decision Works on basis that rational decision

maker will choose the option that maker will choose the option that maximises their utility (the desirability maximises their utility (the desirability or value attached to a decision or value attached to a decision outcome)outcome)

What is decision analysis?What is decision analysis?

““Decision analysis is a systematic, Decision analysis is a systematic, explicit, quantitative way of making explicit, quantitative way of making decisions in health care that can … decisions in health care that can … lead to both enhanced lead to both enhanced communication about clinical communication about clinical controversies and better decisions.” controversies and better decisions.” (Hunink, Glasziou et al, 2001, p.3.)(Hunink, Glasziou et al, 2001, p.3.)

What is decision analysis?What is decision analysis?

Assists in comprehension of problemAssists in comprehension of problem Divides logical structure of decision Divides logical structure of decision

problem into its componentsproblem into its components Uses evidence in the form of probabilitiesUses evidence in the form of probabilities Analysed individuallyAnalysed individually Recombined systematicallyRecombined systematically

Suggests a decisionSuggests a decision Use of decision trees as a way of Use of decision trees as a way of

structuring the problemstructuring the problem

Decision Analysis: The Decision Analysis: The PROACTIVE frameworkPROACTIVE framework

Make problem and its objectives explicitMake problem and its objectives explicit List alternative actionsList alternative actions How actions alter subsequent events with How actions alter subsequent events with

probabilities, values and trade-offsprobabilities, values and trade-offs Synthesise balance of benefits and harms of Synthesise balance of benefits and harms of

each alternativeeach alternativePProblem, roblem, RReframe, eframe, OObjectives, bjectives, AAlternatives, lternatives, CConsequences and chances, onsequences and chances, TTrade-offs, rade-offs, IIntergrate, ntergrate, VValue, alue, EExplore and evaluatexplore and evaluate

Normally uses framework of decision treesNormally uses framework of decision trees

Problem and ObjectivesProblem and Objectives

Need to ensure addressing the right Need to ensure addressing the right problemproblem Define the Define the pproblemroblem RReframe the problem from other eframe the problem from other

perspectivesperspectives Identify fundamental Identify fundamental oobjectives for any bjectives for any

course of actioncourse of action

Problem and ObjectivesProblem and Objectives

What would happen if I did nothing?What would happen if I did nothing? Outcomes avoid/achieve Outcomes avoid/achieve

ReframingReframing What are the limits on resources, patient What are the limits on resources, patient

perspectives, provider perspectives, perspectives, provider perspectives, policy maker?policy maker?

ObjectivesObjectives What elements are of most concern to What elements are of most concern to

the patient/population?the patient/population?

An ExampleAn Example Should a health care worker who Should a health care worker who

has a needlestick injury be given has a needlestick injury be given HIV prophylaxis treatment?HIV prophylaxis treatment? HIV an incurable chronic illnessHIV an incurable chronic illness There is a risk of infection from There is a risk of infection from

needlestick injuryneedlestick injury Prophylaxis treatment can be given to Prophylaxis treatment can be given to

prevent HIV infection, but side effects prevent HIV infection, but side effects can be problematiccan be problematic

Public Health Service guidelines for the management of health-care worker exposures to HIV and recommendations for postexposure prophylaxis. Centers for Disease Control and Prevention. MMWR – Morbidity and Mortality Weekly Report 47(RR-7): 1-33, 1998

Problem and ObjectivesProblem and Objectives ProblemProblem

Should all health care workers who receive a needlestick Should all health care workers who receive a needlestick injury receive prophylaxis treatment for HIV?injury receive prophylaxis treatment for HIV?

ReframeReframe What is the risk of infection after needlestick? What What is the risk of infection after needlestick? What

drugs are available for prophylaxis? How effective are drugs are available for prophylaxis? How effective are they? What are their side effects? they? What are their side effects?

ObjectiveObjective To determine if a health care worker who has a To determine if a health care worker who has a

needlestick injury should have prophylaxis treatment for needlestick injury should have prophylaxis treatment for HIV HIV

Alternatives, Consequences Alternatives, Consequences and Trade-offsand Trade-offs

Range of reasonable Range of reasonable aalternativeslternatives Three categories; Three categories;

Watchful waitingWatchful waiting InterventionIntervention More information before decidingMore information before deciding

Can be illustrated using a decision treeCan be illustrated using a decision tree

The structure of a decision The structure of a decision treetree

Square nodeSquare node Decision nodeDecision node Represents choice Represents choice

between actionsbetween actions Circle nodeCircle node

Chance nodeChance node Represents Represents

uncertaintyuncertainty Potential outcomes Potential outcomes

of each decisionof each decision

Consequences and chancesConsequences and chances

CConsequences of each decision onsequences of each decision option and chance of event occurringoption and chance of event occurring Short term and long termShort term and long term

Need best available evidenceNeed best available evidence Includes risks and benefits of Includes risks and benefits of

interventionsinterventions Natural history of diseaseNatural history of disease Accuracy and interpretation of Accuracy and interpretation of

diagnostic test informationdiagnostic test information

Example: AlternativesExample: Alternatives

Alternatives for treating needlestick Alternatives for treating needlestick injuries include:injuries include: No prophylaxisNo prophylaxis Use of prophylaxis selectively Use of prophylaxis selectively

dependent on injury and perceived risk dependent on injury and perceived risk from patientfrom patient

Routine prophylaxis treatment for all Routine prophylaxis treatment for all injuriesinjuries

Consequences and chances: Balance sheetConsequences and chances: Balance sheet

BenefitBenefit HarmHarm

No No prophylaxisprophylaxis

No side effects from No side effects from treatmenttreatment

No unnecessary No unnecessary treatmenttreatment

Risk of developing HIVRisk of developing HIV

Selective Selective prophylaxisprophylaxis

Reduced risk of Reduced risk of developing HIVdeveloping HIV

Risk of developing HIV if Risk of developing HIV if injury/patient not injury/patient not perceived to be high riskperceived to be high risk

Side effects from treatmentSide effects from treatment

Prophylaxis may not workProphylaxis may not work

Routine Routine prophylaxisprophylaxis

Reduced risk of Reduced risk of developing HIVdeveloping HIV

May have unnecessary May have unnecessary treatmenttreatment

Side effects from treatmentSide effects from treatment

Prophylaxis may not workProphylaxis may not work

Modelling the consequencesModelling the consequences

ChancesChances

Use probability or chance of events Use probability or chance of events occurringoccurring

For each ‘branch’ in the decision tree, For each ‘branch’ in the decision tree, values have to add up to 1 or 100%values have to add up to 1 or 100%

Specific measures of the uncertainty Specific measures of the uncertainty associated with the decisionassociated with the decision

Probabilities should come from good Probabilities should come from good quality research evidencequality research evidence

Identifying the chancesIdentifying the chances Average risk for HIV transmission after percutaneous Average risk for HIV transmission after percutaneous

exposure to HIV infected blood is approximately 0.3%exposure to HIV infected blood is approximately 0.3% Effectiveness of prophylaxis difficult to estimate – a Effectiveness of prophylaxis difficult to estimate – a

case control study indicated that prophylaxis reduced case control study indicated that prophylaxis reduced odds of HIV infection by 81%. (If change this to odds of HIV infection by 81%. (If change this to percentages – if take prophylaxis 5% chance will percentages – if take prophylaxis 5% chance will develop HIV)develop HIV)

Side effects include nausea/vomiting, malaise/fatigue, Side effects include nausea/vomiting, malaise/fatigue, headache, myalgia, abdominal pain, diarrohea. headache, myalgia, abdominal pain, diarrohea. Probability of getting a side effect 50-75%. (Figure Probability of getting a side effect 50-75%. (Figure used 63%)used 63%)Public Health Service guidelines for the management of health-care worker exposures to HIV and

recommendations for postexposure prophylaxis. Centers for Disease Control and Prevention. MMWR – Morbidity and Mortality Weekly Report 47(RR-7): 1-33, 1998.

Cardo, D., Culver, D. et al (1997) A case-control study of HIV seroconversion in health care workers after percutaneous exposure. New England Journal of Medicine 337:21, 1485-1490

Probabilities in the treeProbabilities in the tree

Identifying and estimating the Identifying and estimating the value of Trade-offsvalue of Trade-offs

When there is more than one type of When there is more than one type of consequence – valuation importantconsequence – valuation important

Trade-offs between benefits and potential Trade-offs between benefits and potential harms of consequencesharms of consequences

Need clarification of the values involvedNeed clarification of the values involved Choice of intervention will often depend Choice of intervention will often depend

on the values of the decision makeron the values of the decision maker When considering values, need to When considering values, need to

consider whether individual or societalconsider whether individual or societal

Measuring valuesMeasuring values Need a strategy that weighs harms and benefits Need a strategy that weighs harms and benefits

explicitly in accordance with values of explicitly in accordance with values of population/individualpopulation/individual

Types of outcomeTypes of outcome Two possible outcomesTwo possible outcomes – – no need for explicit value no need for explicit value

assessment as chose the strategy that gives highest probability of assessment as chose the strategy that gives highest probability of better outcomebetter outcome

Single-attribute case Single-attribute case – – spectrum of outcomes from least to spectrum of outcomes from least to most preferred (e.g. survival time)most preferred (e.g. survival time)

Multi-attribute caseMulti-attribute case – – two or more dimensions or values two or more dimensions or values (e.g. life expectancy and quality of life). Easier if can be (e.g. life expectancy and quality of life). Easier if can be measured on a single, generic scalemeasured on a single, generic scale

Measuring values Measuring values Utility (value) measures different from quality of life Utility (value) measures different from quality of life

measures – measures – reflect how respondent values a state of reflect how respondent values a state of health, not just the characteristics of the health statehealth, not just the characteristics of the health state

Utility scale – Utility scale – can be averaged out in a decision tree can be averaged out in a decision tree without distorting preferences of individual represented. without distorting preferences of individual represented. Normally measured from 0 = DEATH to 1 = PERFECT Normally measured from 0 = DEATH to 1 = PERFECT HEALTHHEALTH

Quality Adjusted Life Years (QALY) commonly used Quality Adjusted Life Years (QALY) commonly used for population utility measures – for population utility measures – 1 year in perfect 1 year in perfect health = 1 QALY. Health states measured against this (e.g. health = 1 QALY. Health states measured against this (e.g. 2 years in health rated as 0.5 of perfect health = 1 QALY) 2 years in health rated as 0.5 of perfect health = 1 QALY) Considers quantity and quality of life.Considers quantity and quality of life.

Measuring valuesMeasuring values

Rating scaleRating scale Global measureGlobal measure Easily explained and easy to measureEasily explained and easy to measure Not a true utilityNot a true utility

Standard GambleStandard Gamble Grounded in expected utility theoryGrounded in expected utility theory Assesses utility for a health state by asking how Assesses utility for a health state by asking how

high a risk of death would accept to improve ithigh a risk of death would accept to improve it Ask to choose between life in given state and a Ask to choose between life in given state and a

gamble between perfect health and deathgamble between perfect health and death

Measuring valuesMeasuring values Time trade-offTime trade-off

Utility assessed by asking how much time would Utility assessed by asking how much time would give up to improve itgive up to improve it

Choose between set length of life in given health Choose between set length of life in given health state and shorter length of life in perfect healthstate and shorter length of life in perfect health

Utility given by ratio of shorter to longer life Utility given by ratio of shorter to longer life expectancyexpectancy

Other techniquesOther techniques Willingness to payWillingness to pay Health indexes (e.g. Health Utilities Index (HUI), Health indexes (e.g. Health Utilities Index (HUI),

EuroQol). Use mapping rules to translate QOL EuroQol). Use mapping rules to translate QOL measures into utilitiesmeasures into utilities

Calculating expected utilityCalculating expected utility

Values are placed in decision tree by Values are placed in decision tree by appropriate outcomesappropriate outcomes

Expected value for each branch calculated Expected value for each branch calculated by multiplying utility with probabilityby multiplying utility with probability

Expected values for each branch of tree Expected values for each branch of tree added together to give EU for each added together to give EU for each decision optiondecision option

Depending on nature of values, option Depending on nature of values, option with highest/lowest value is the option that with highest/lowest value is the option that should be takenshould be taken

Example: ValuesExample: Values

‘‘Off the shelf’ measuresOff the shelf’ measures Existing preference scores associated with Existing preference scores associated with

HIV infection and some side effectsHIV infection and some side effects Preference scores for HIV range from 0.5 – 0.75Preference scores for HIV range from 0.5 – 0.75 Nausea and vomiting – 0.9863Nausea and vomiting – 0.9863 Diarrohea – 0.81Diarrohea – 0.81 Abdominal pain – 0.9863Abdominal pain – 0.9863

Values used in model – HIV infection 0.5, Values used in model – HIV infection 0.5, side effects 0.9, no infection 1.0. Infection side effects 0.9, no infection 1.0. Infection and side effects – 0.4 (my value)and side effects – 0.4 (my value)

Bell, C.M., Richard, H. Et al (2001) A comprehensive catalog of preference scores from published cost-utility analyses. Medical Decision Making 21(4), 288-294

Full analysisFull analysis

Explore assumptionsExplore assumptions

Necessary if numbers used in Necessary if numbers used in analysis are uncertainanalysis are uncertain

Allows you to examine the effect Allows you to examine the effect different values will have on outcomedifferent values will have on outcome

Known as sensitivity analysisKnown as sensitivity analysis vary uncertain variables over range that vary uncertain variables over range that

is considered plausibleis considered plausible Can calculate effect of uncertainty on Can calculate effect of uncertainty on

decisiondecision

ExampleExample

Varied probabilitiesVaried probabilities Risk for HIV transmission after Risk for HIV transmission after

percutaneous exposure to HIV infected percutaneous exposure to HIV infected blood CI- 0.2%-0.5%blood CI- 0.2%-0.5%

Probability of getting a side effect 50-Probability of getting a side effect 50-75%. 75%.

Varied utilitiesVaried utilities Preference associated with HIV Preference associated with HIV

infection 30 - 75infection 30 - 75

Sensitivity Analysis Sensitivity Analysis If the probability of If the probability of

no side effects is no side effects is less than 0.432, less than 0.432, then optimum then optimum decision is no decision is no prophylaxisprophylaxis

If the probability of If the probability of no side effects is no side effects is greater than 0.432, greater than 0.432, then the optimum then the optimum decision is decision is prophylaxisprophylaxis

Sensitivity AnalysisSensitivity Analysis

Optimum decision also affected by Optimum decision also affected by the probability of getting side effects the probability of getting side effects from the treatmentfrom the treatment

Varying the probability of getting Varying the probability of getting HIV, or the preferences associated HIV, or the preferences associated with having HIV have no effect on the with having HIV have no effect on the optimum decisionoptimum decision

Benefits of Decision AnalysisBenefits of Decision Analysis

Makes all assumptions in a decision Makes all assumptions in a decision explicitexplicit

Allows examination of the decision Allows examination of the decision process usedprocess used

Often insight gained during process Often insight gained during process more important than the actual more important than the actual numbers usednumbers used

Limitations of decision analysisLimitations of decision analysis

Probability estimatesProbability estimates often data sets needed to estimate probability don’t often data sets needed to estimate probability don’t

existexist Subjective probability estimates are open to bias: Subjective probability estimates are open to bias:

overconfidence & heuristicsoverconfidence & heuristics

Utility measuresUtility measures often ask individuals to rate a state of health that they often ask individuals to rate a state of health that they

have no experience ofhave no experience of Different techniques will result in different numbersDifferent techniques will result in different numbers Subject to framing effectsSubject to framing effects