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Table 3 Performance of Greedy and Optimal Algorithm at Different Levels of Caliper for a 1:2 Match

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 Number Cases/Controlsb Mean Distance Sum of Distance
Greedy 1 1 8 7/6/1 1.02 8.15
Optimal 1 1 8 7/6/1 1.02 8.15
Greedy 2 2 28 21/14/7 1.90 53.29
Optimal 2 2 28 21/14/7 1.90 53.29
Greedy 3 3 38 26/14/12 2.28 86.54
Optimal 3 3 38 26/14/12 2.28 86.63
Greedy 4 4 48 32/16/16 2.87 137.9
Optimal 4 4 49 33/17/16 2.97 145.7
Greedy 5a 5 56 34/12/22 3.47 194.4
Optimal 5a 5 60 36/12/24 3.91 234.4
Greedy 6 6 62 37/12/25 3.98 247.1
Optimal 6 6 67 39/11/28 4.27 286.1
  1. aCaliper 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
  3. bThere are three numbers listed in this column, for example 7/6/1 means seven cases were matched, six cases matched to 1:1, so six controls; and one case matched to 1:2, so two controls. This gives a total of eight matched pairs