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Table 3 Illustration of the effect of collapsing exposure categories

From: Spurious interaction as a result of categorization

X1=1 X1=2
X 2 Diseased Not diseased Total RR X 2 Diseased Not diseased Total RR
1 20 380 400 1.0 1 5 95 100 1.0
2 30 270 300 2.0 2 20 180 200 2.0
3 30 170 200 3.0 3 45 255 300 3.0
4 20 80 100 4.0 4 80 320 400 4.0
  1. The table gives the true situation