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Randomization and Comparative Designs

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?.

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Randomization and Comparative Designs

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  1. Randomization and Comparative Designs Oncology Journal Club April 5, 2002

  2. Comparative Designs • “Compare”: need more than one group • Different types • historical control • two+ treatment groups • treatment and placebo groups • “Phase III”

  3. 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?

  4. 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!

  5. 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.

  6. 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

  7. 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.

  8. 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

  9. 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

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