decision analysis. what is decision analysis? based on expected utility theory based on expected...
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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