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Practical and methodological issues€¦ · number generation and an adequate allocation...

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Practical and methodological issues M. Gülmezoglu Department of Reproductive Health and Research WHO Geneva
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Page 1: Practical and methodological issues€¦ · number generation and an adequate allocation concealment 45% of double-blind trials described similarity 26% of double-blind trials provided

Practical and methodological issues

M. GülmezogluDepartment of Reproductive Health and Research

WHO Geneva

Page 2: Practical and methodological issues€¦ · number generation and an adequate allocation concealment 45% of double-blind trials described similarity 26% of double-blind trials provided

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

Page 3: Practical and methodological issues€¦ · number generation and an adequate allocation concealment 45% of double-blind trials described similarity 26% of double-blind trials provided

Randomized Controlled Trial

Unpredictable allocation sequence (random)

EXPT CTRL

Outcome

Page 4: Practical and methodological issues€¦ · number generation and an adequate allocation concealment 45% of double-blind trials described similarity 26% of double-blind trials provided

Types of interventions

PharmacologicalSurgicalPsychologicalEducationalSocial

Page 5: Practical and methodological issues€¦ · number generation and an adequate allocation concealment 45% of double-blind trials described similarity 26% of double-blind trials provided

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)

Page 6: Practical and methodological issues€¦ · number generation and an adequate allocation concealment 45% of double-blind trials described similarity 26% of double-blind trials provided

RCT designs

ParallelSuccessive treatment– Replacement therapy– Cross-over

Page 7: Practical and methodological issues€¦ · number generation and an adequate allocation concealment 45% of double-blind trials described similarity 26% of double-blind trials provided

When are RCTs appropriate?

EffectivenessSmall - moderate effects

Page 8: Practical and methodological issues€¦ · number generation and an adequate allocation concealment 45% of double-blind trials described similarity 26% of double-blind trials provided

Why are RCTs important?

Results of RCTs provide the most secure basis for valid causal inferences– Control for confounders – Prevent selection bias

Page 9: Practical and methodological issues€¦ · number generation and an adequate allocation concealment 45% of double-blind trials described similarity 26% of double-blind trials provided

Confounder

A variable independently associated with the intervention or exposureRandom allocation enables– controlling for known confounders– random distribution of unknown

confounders in treatment groups

Page 10: Practical and methodological issues€¦ · number generation and an adequate allocation concealment 45% of double-blind trials described similarity 26% of double-blind trials provided

ConfounderConfounder

Maternal physical activity and pregnancy outcome (low birth weight)– Age– Nutritional status– Obstetrical history

Page 11: Practical and methodological issues€¦ · number generation and an adequate allocation concealment 45% of double-blind trials described similarity 26% of double-blind trials provided

Bias

A systematic error or deviation in results or inferences

Page 12: Practical and methodological issues€¦ · number generation and an adequate allocation concealment 45% of double-blind trials described similarity 26% of double-blind trials provided

Types of bias

Selection bias

Performance bias

Attrition bias

Detection bias

Page 13: Practical and methodological issues€¦ · number generation and an adequate allocation concealment 45% of double-blind trials described similarity 26% of double-blind trials provided

Prevention of selection bias

Randomization (Generation of an unpredictable sequence of allocation)

Allocation concealment

Page 14: Practical and methodological issues€¦ · number generation and an adequate allocation concealment 45% of double-blind trials described similarity 26% of double-blind trials provided

Concealment of allocation

Centralised

Coded, identical containers

On-site computer system

Sequentially numbered, sealed, opaque envelopes

Page 15: Practical and methodological issues€¦ · number generation and an adequate allocation concealment 45% of double-blind trials described similarity 26% of double-blind trials provided

Concealment of allocation

Inadequate– Alternation– Day of birth– Case record no.– when nothing

reportedNot used– Open list

Page 16: Practical and methodological issues€¦ · number generation and an adequate allocation concealment 45% of double-blind trials described similarity 26% of double-blind trials provided

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

Page 17: Practical and methodological issues€¦ · number generation and an adequate allocation concealment 45% of double-blind trials described similarity 26% of double-blind trials provided

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

Page 18: Practical and methodological issues€¦ · number generation and an adequate allocation concealment 45% of double-blind trials described similarity 26% of double-blind trials provided

Performance bias

Protection: Blinding– Providers– Patients

More important when subjective outcome measures are used

Page 19: Practical and methodological issues€¦ · number generation and an adequate allocation concealment 45% of double-blind trials described similarity 26% of double-blind trials provided

Attrition bias

Bias due to differences between groups in losses of participants from the study– withdrawals– dropouts– protocol deviations

Page 20: Practical and methodological issues€¦ · number generation and an adequate allocation concealment 45% of double-blind trials described similarity 26% of double-blind trials provided

Detection bias

Were persons responsible for outcome assessments unaware of the assigned therapy?

Page 21: Practical and methodological issues€¦ · number generation and an adequate allocation concealment 45% of double-blind trials described similarity 26% of double-blind trials provided

How to conduct RCTs

Careful planning essentialProtocol with a systematic reviewResources needed– staff– money– expert support (statistician, trialist)Institutional support

Page 22: Practical and methodological issues€¦ · number generation and an adequate allocation concealment 45% of double-blind trials described similarity 26% of double-blind trials provided

Design of an RCT

Question/hypothesisMethods– Randomization process– Power calculation/sample size– Eligibility (inclusion/exclusion criteria)– Outcomes

PrimarySecondary

Page 23: Practical and methodological issues€¦ · number generation and an adequate allocation concealment 45% of double-blind trials described similarity 26% of double-blind trials provided

Randomization process

Generation of allocation sequence(Concealment of) allocation

Page 24: Practical and methodological issues€¦ · number generation and an adequate allocation concealment 45% of double-blind trials described similarity 26% of double-blind trials provided

Analysis

Baseline comparisons– descriptive statisticsOutcomes– intention-to-treat– measures of effectiveness

relative riskodds ratioNumber needed to treat

Page 25: Practical and methodological issues€¦ · number generation and an adequate allocation concealment 45% of double-blind trials described similarity 26% of double-blind trials provided

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

Page 26: Practical and methodological issues€¦ · number generation and an adequate allocation concealment 45% of double-blind trials described similarity 26% of double-blind trials provided

Reporting

CONSORT guidelines– Identify in the title RCT– Structured abstract– Methods

ParticipantsInterventionsOutcomesPlanned analyses

.

.

Page 27: Practical and methodological issues€¦ · number generation and an adequate allocation concealment 45% of double-blind trials described similarity 26% of double-blind trials provided

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 =

Page 28: Practical and methodological issues€¦ · number generation and an adequate allocation concealment 45% of double-blind trials described similarity 26% of double-blind trials provided

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

Page 29: Practical and methodological issues€¦ · number generation and an adequate allocation concealment 45% of double-blind trials described similarity 26% of double-blind trials provided

Conclusion

RCTs need– careful planning– careful execution– comprehensive reporting


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