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A medical study compares the efficacy of two drugs across two clinics. In Clinic 1, Drug A has a 70% success rate and Drug B has a 60% success rate. In Clinic 2, Drug A has a 30% success rate and Drug B has a 20% success rate.

However, when the data from both clinics are combined, Drug B appears to have a higher overall success rate than Drug A. Which statistical phenomenon is demonstrated, and what is the underlying cause?

  1. The Ecological Fallacy; it occurs because the researcher is incorrectly inferring individual success from group-level averages.
  2. Selection Bias; it occurs because the patients were not randomly assigned to the clinics, leading to non-representative samples.
  3. Simpson's Paradox; it occurs because a lurking variable (the clinic size) is disproportionately distributed across the drug groups.
  4. Berkson's Paradox; it occurs because the observation is limited to a specific sub-population in a clinical setting.

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