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Why are some trials not randomized?

Learn why some trials are not randomized, the advantages and disadvantages of randomized controlled trials (RCTs), cohort studies, and case-control studies. Explore different study designs and their applications in medical research.

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Why are some trials not randomized?

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  1. Why are some trials not randomized? • Inexperienced researchers • May be impractical or unethical • Design flaws may invalidate the conclusions

  2. Questions addressed by RCT • Is drug A better than drug B or placebo for treatment of a particular condition • Is written or verbal advice better to help patients make decisions about treatment options

  3. RCT: advantages • Allows rigorous evaluation of a single variable in a defined patient group • Prospective • Designed to test the null hypothesis • Reduces bias • Allows for meta-analysis

  4. RCT: disadvantages • Expensive and time consuming!! • Often not enough patients • Often patients not followed for long enough • Most funding comes from government or industry • Surrogate endpoints often used • Failure to randomize all eligible patients

  5. Cohort studies • 2 or more groups selected based on differences in exposure to a particular agent (medication, environmental toxin, etc.) • Groups are followed to see who develops disease • Cohort studies can be used to define risk factors

  6. Case-control studies • Patients with a particular disease or condition are identified (“case”) and matched with controls (different disease, general population, relatives) • Data are collected about the two groups (medical records, interview) and compared

  7. Case control studies and cohort studies usually address what may cause a disease (etiology) rather than how to treat a disease • Can the case-control design show causality? • Case-control studies are retrospective

  8. Examples of case control studies • Sleeping position and sudden infant death syndrome • Brain tumors and cell phone use

  9. Cross sectional surveys • Interview a representative sample of subjects • Collect data at time point of interview with or without reference retrospectively to events in the past • Examples?

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