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Table 2 Associations between type of surgery and surgical outcome.

From: Simpson’s Paradox is suppression, but Lord’s Paradox is neither: clarification of and correction to Tu, Gunnell, and Gilthorpe (2008)

 Open surgeryPercutaneous nephrolithotomy 
Association between type of surgery and surgical outcome, disregarding kidney-stone size
 Failure7761 
 Success273289 
 Total350350 
Percentage success78%83%Positive association
 Large stoneSmall stone 
Open surgeryPercutaneous nephrolithotomyOpen surgeryPercutaneous nephrolithotomy
Association between type of surgery and surgical outcome for each kidney-stone size
 Failure7125636 
 Success1925581234 
 Total2638087270 
 Percentage success73%69%93%87%Negative associations
  1. Surgical outcome coded 0 = failure, 1 = success; type of surgery coded 0 = open surgery, 1 = percutaneous nephrolithotomy; kidney-stone size coded 0 = large stone, 1 = small stone