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Table 1 Individual vs. ecologic data

From: Bias magnification in ecologic studies: a methodological investigation

  Individual (interior cells) Ecologic (margins)
  exposed unexposed sum exposed unexposed sum
cases 16 12 28 ? ? 28
noncases 24 48 72 ? ? 72
total 40 60 100 40 60 100
risks 0.4 0.2   X 0.40  
RD 0.2    Y 0.28  
     n 100  
  1. Individual-level information on exposure and outcome are shown by the interior of a two-by-two table; they are summarized by the risks in the unexposed and exposed and the risk difference (RD). Ecologic studies possess only the margins of the table, summarized by the average exposure X, average risk Y and group size n.