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Table 2 Performance of Greedy and Optimal Algorithm at Different Levels of Caliper

From: Methodologic considerations in the design and analysis of nested case-control studies: association between cytokines and postoperative delirium

Match Algorithm Age Caliper GCP Caliper Number of Pairs Mean Distance Sum of Distance
Greedy 1 1 7 0.99 6.90
Optimal 1 1 7 0.99 6.90
Greedy 2 2 21 1.79 37.51
Optimal 2 2 21 1.76 36.89
Greedy 3 3 26 2.06 53.63
Optimal 3 3 26 2.05 53.48
Greedy 4 4 32 2.68 85.81
Optimal 4 4 34 2.99 101.7
Greedy 5* 5 34 3.01 102.45
Optimal 5* 5 39 3.79 147.79
  1. *Caliper is defined to be the minimum allowable difference between the case and the control. In our study, we used a caliper of five for age and GCP, and zero for the other four categorical variables
  2. GCP general cognitive performance