practical and methodological issues€¦ · number generation and an adequate allocation...
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Practical and methodological issues
M. GülmezogluDepartment of Reproductive Health and Research
WHO Geneva
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Definition
A controlled experiment to assess the safety and efficacy of treatments for human diseases and health problems in which, treatments are assigned at random
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Randomized Controlled Trial
Unpredictable allocation sequence (random)
EXPT CTRL
Outcome
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Types of interventions
PharmacologicalSurgicalPsychologicalEducationalSocial
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RCTs
PHASE I .. .PHASE II ……………………..PHASE IIIPHASE IV
Initial evaluation in human subjects (20-100)Potential effectiveness, optimal method, route (100-200)Evaluate the new treatmentEvaluate long term effects (postmarketing surveillance)
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RCT designs
ParallelSuccessive treatment– Replacement therapy– Cross-over
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When are RCTs appropriate?
EffectivenessSmall - moderate effects
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Why are RCTs important?
Results of RCTs provide the most secure basis for valid causal inferences– Control for confounders – Prevent selection bias
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Confounder
A variable independently associated with the intervention or exposureRandom allocation enables– controlling for known confounders– random distribution of unknown
confounders in treatment groups
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ConfounderConfounder
Maternal physical activity and pregnancy outcome (low birth weight)– Age– Nutritional status– Obstetrical history
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Bias
A systematic error or deviation in results or inferences
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Types of bias
Selection bias
Performance bias
Attrition bias
Detection bias
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Prevention of selection bias
Randomization (Generation of an unpredictable sequence of allocation)
Allocation concealment
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Concealment of allocation
Centralised
Coded, identical containers
On-site computer system
Sequentially numbered, sealed, opaque envelopes
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Concealment of allocation
Inadequate– Alternation– Day of birth– Case record no.– when nothing
reportedNot used– Open list
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Effect size increases with reduced concealment
Nonrandomized studies yield larger estimates of treatment effects than RCTs
RCTs using inadequate concealment of allocation yield larger estimates of treatment effects than adequately concealed RCTs
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Local sealed envelope randomisation in a Local sealed envelope randomisation in a multicentremulticentre trial: a cautionary tale. trial: a cautionary tale. Kennedy A, Grant A.Kennedy A, Grant A.
Surgical trialSealed envelopesMedian age of patients allocated to EXPT significantly higher (59 vs 63 y)For 3 surgeons (57 vs 72)No differences existed after switching to central allocation
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Performance bias
Protection: Blinding– Providers– Patients
More important when subjective outcome measures are used
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Attrition bias
Bias due to differences between groups in losses of participants from the study– withdrawals– dropouts– protocol deviations
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Detection bias
Were persons responsible for outcome assessments unaware of the assigned therapy?
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How to conduct RCTs
Careful planning essentialProtocol with a systematic reviewResources needed– staff– money– expert support (statistician, trialist)Institutional support
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Design of an RCT
Question/hypothesisMethods– Randomization process– Power calculation/sample size– Eligibility (inclusion/exclusion criteria)– Outcomes
PrimarySecondary
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Randomization process
Generation of allocation sequence(Concealment of) allocation
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Analysis
Baseline comparisons– descriptive statisticsOutcomes– intention-to-treat– measures of effectiveness
relative riskodds ratioNumber needed to treat
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Reporting - Problems
49% specified an adequate method of random number generation15% reported both adequate method of random number generation and an adequate allocation concealment45% of double-blind trials described similarity26% of double-blind trials provided information on the allocation scheduleExclusions after randomization usually ignored
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Reporting
CONSORT guidelines– Identify in the title RCT– Structured abstract– Methods
ParticipantsInterventionsOutcomesPlanned analyses
.
.
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CONSORT statementTrial outline
Loss to follow-upn =
Outcome availablen =
Randomized to treatment An =
Loss to follow-upn =
Outcome availablen =
Randomized to treatment Bn =
Gave informed consentn =
Eligiblen =
Screenedn =
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Small trials
Freiman 1978 NEJM71 negative trials (no significant effect)67 had < 90% power of detecting a 25 % change50 would have missed a 50 % change with the new treatment
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Conclusion
RCTs need– careful planning– careful execution– comprehensive reporting