LECTURE 07 2011

LECTURE 07 2011 - Blinding or Masking of Treatments and...

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Blinding or Masking of Treatments and Other Aspects of the Trial
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Two Important Methods for Removing Bias in Clinical Trials 1. Randomization 2. Blinding Treatment application Endpoint assessment
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Bias (def.) - A systematic error usually introduced (conscious or unconscious) by investigator / trial participant which leads to incorrect estimates of the treatment effect
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Blinding of Treatments Feature of design to eliminate bias associated with physician/patient being aware of treatment that is given Note : different from type of bias that randomization prevents
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Examples of Bias Eliminated or Removed with Blinding Differential/preferential ancillary/compensatory treatment Differential ascertainment/diagnosis of endpoints (primary outcomes and toxicities) Differential compliance/visit attendance/record keeping
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Overview of Trials in Pregnancy or Childbirth * 250 trials; authors studied the association of methodological rigor with treatment effect as measured by odds ratio (i.e., interaction of treatment effect with quality measure) Two significant predictors: 1) unclear allocation concealment resulted in more extreme treatment differences than adequate measures (p<0.001); and 2) trials that were not double-blind resulted in more extreme treatment differences than double- blind studies (p=0.01). * Schulz et al., JAMA, pp.408-412, 1995.
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Pocock identifies four areas to consider to determine whether blinding is feasible 1) Ethics - undue harm to patient 2) Practicality - similarity of treatments 3) Avoidance of bias - How much bias? 4) Compromise – partial blinding
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MRC Trial on Tuberculosis MRC committee considered whether the trial on streptomycin should be blinded and whether the investigator should be allowed to modify therapy (e.g., collapse therapy). Use of placebo would have required IM injection 4xday for 4 months Hill argued “no need in the search for precision to throw common sense out the window”
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Blinding 1) of patient 2) of treatment team 3) of endpoint assessment (e.g., endpoint review committee)
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Blinding of Treatments Non-blind - Investigator and patient know treatment assigned (“open label”) Single-blind - Investigator knows treatment assigned but patient does not Double-blind - Neither investigator nor patient knows treatment assigned General view - Double-blind > single blind > non-blind
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Other Blinding Considerations 1. Accumulating data: investigators should be blinded; external data monitoring committee (DMC) should not be 2. Some argue DMC should be blinded and only codes should be used. This is sometimes referred to as a triple blind study (more on that later) 3. Study (protocol) statistician as well as investigators 4. Data management staff
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This note was uploaded on 11/21/2011 for the course PUBH 7420 taught by Professor Ph7420 during the Spring '07 term at Minnesota.

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LECTURE 07 2011 - Blinding or Masking of Treatments and...

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