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Randomization and Comparative Trials






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Randomization and Comparative Trials Randomization and Comparative Trials Presentation Transcript

  • Randomization and Comparative Designs Oncology Journal Club April 5, 2002
  • Comparative Designs
    • “Compare”: need more than one group
    • Different types
      • historical control
      • two+ treatment groups
      • treatment and placebo groups
    • “Phase III”
  • Was this study comparative?
    • What are the “groups” that are being compared?
    • Treatment 1 vs. treatment 2?
    • Was it randomized?
      • What was were they randomized to?
      • Did they show a difference in the two groups under consideration?
      • Did they show that the groups being compared were comparable with regard to pertinent factors?
    View slide
  • Randomization
    • Why? What’s the big deal?
    • Reduces potential for bias
    • “Ensures” that groups being compared are likely to be similar to each other.
    • Example of violation of randomization bias:
      • selection bias: the physician decides which patients are assigned to which treatment
      • i.e. physician decides which patients get high versus low radiotherapy!
    View slide
  • Randomization
    • What if physicians tend to give sicker patients less radiotherapy?
    • Now, there is a “correlation” between being sick and treatment.
    • Is it so strange to imagine that the sicker patients would tend to have shorter survival?
    • Now that they have “confounded” sick status with treatment, they CANNOT conclude anything about treatment.
  • Randomization
    • Idea of Confounders : many variables may be associated with outcome. By randomly assigning individuals to treatment groups, we decrease likelihood of making an error due to a confouding variable
  • Randomization
    • Randomization to low versus high radiotherapy WOULD have made illness and treatment independent.
    • How could this have been helped?
      • Inclusion/exclusion criteria so that only kids who were “healthy” enough could receive full dose
      • Stratify by stage: ensure that comparable numbers of sick and less sick kids are in each arm.
  • Final Comments on Randomization
    • It does not guarantee that groups are “the same,” but the principle is that for large numbers of patients, the groups will even out.
    • For small studies, might be a good idea to stratify to really ensure balance.
    • Randomization isn’t always truly random
      • blocking
      • stratification
  • Final Comments on Comparative Trials
    • Selection bias: not just physician choice
      • center (e.g. multi-center study)
      • patient (think about ITT vs. actual received)
    • Blinding/Masking:
      • when possible, it is generally a good idea for patient (blinded) or patient and physician (double-blinded) to not know which group patient is assigned to
      • avoids sub-concious effects
      • avoids cross-over