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Table 4 Multiplication factors for the required sample sizes accounting for clustering at group level

From: Sampling strategies to measure the prevalence of common recurrent infections in longitudinal studies

  52 visits 20 visits 12 visits 6 visits 4 visits
Model scenario 1 (LS)      
no clustering 1.0 1.4 1.9 3.3 4.8
Cluster size n = 5      
   ICC = 0.04 1.0 1.4 1.8 3.0 4.3
   ICC = 0.1 1.0 1.3 1.7 2.7 3.8
   ICC = 0.3 1.0 1.2 1.4 2.1 2.8
Cluster size n = 50      
   ICC = 0.005 1.0 1.3 1.8 2.9 4.2
   ICC = 0.02 1.0 1.2 1.5 2.2 3.0
   ICC = 0.1 1.0 1.1 1.2 1.4 1.7
Model scenario 2 (LL)      
no clustering 1.0 1.1 1.4 2.2 2.9
Cluster size n = 5      
   ICC = 0.04 1.0 1.1 1.4 2.0 2.7
   ICC = 0.1 1.0 1.1 1.3 1.8 2.4
   ICC = 0.3 1.0 1.1 1.2 1.5 1.9
Cluster size n = 50      
   ICC = 0.005 1.0 1.1 1.3 1.9 2.6
   ICC = 0.02 1.0 1.1 1.2 1.6 2.0
   ICC = 0.1 1.0 1.0 1.1 1.2 1.4
Model scenario 3 (HS)      
no clustering 1.0 1.1 1.3 1.7 2.1
Cluster size n = 5      
   ICC = 0.04 1.0 1.1 1.2 1.6 2.0
   ICC = 0.1 1.0 1.1 1.2 1.5 1.8
   ICC = 0.3 1.0 1.1 1.1 1.3 1.5
Cluster size n = 50      
   ICC = 0.005 1.0 1.1 1.2 1.6 1.9
   ICC = 0.02 1.0 1.1 1.2 1.4 1.6
   ICC = 0.1 1.0 1.0 1.1 1.2 1.3
Model scenario 4 (HL)      
no clustering 1.0 1.1 1.2 1.5 1.8
Cluster size n = 5      
   ICC = 0.04 1.0 1.1 1.2 1.4 1.7
   ICC = 0.1 1.0 1.0 1.1 1.3 1.6
   ICC = 0.3 1.0 1.0 1.1 1.2 1.4
Cluster size n = 50      
   ICC = 0.005 1.0 1.1 1.2 1.4 1.6
   ICC = 0.02 1.0 1.0 1.1 1.2 1.4
   ICC = 0.1 1.0 1.0 1.0 1.1 1.2
  1. The sample size is calculated for a study comparing the mean LP between two groups with a 20% LP reduction in one arm (80% power and p = 0.05). Sampling was simulated as 7 day point prevalence recall at each visit (see Table 3.).