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Table 2 Description of different configurations of sample size in equal and unequal sample size designs.

From: Comparison of three tests of homogeneity of odds ratios in multicenter trials with unequal sample sizes within and among centers

K

Sample size per treatment arm

 

Equal sample size design:

E1: ntot= 160(20:20, 20:20, 20:20, 20:20)

E2: ntot= 400(50:50, 50:50, 50:50, 50:50)

E3: ntot= 800(100:100, 100:100, 100:100, 100:100)

4

Within-center inequality:

W 1 : ntot= 160(10:30, 10:30, 10:30, 10:30)

W 2 : ntot= 400(25:75, 25:75, 25:75, 25:75)

W 3 : ntot= 800(50:150, 50:150, 50:150, 50:150)

 

Among-centers inequality:

A 1 : ntot= 160(10:10, 10:10, 10:10, 50:50)

A 2 : ntot= 400(25:25, 25:25, 25:25, 125:125)

A 3 : ntot= 800(50:50, 50:50, 50:50, 250:250)

 

Equal sample size design:

E 1 : ntot= 240(20:20, 20:20, 20:20, 20:20, 20:20, 20:20)

E 2 : ntot= 600(50:50, 50:50, 50:50, 50:50, 50:50, 50:50)

E 3 : ntot= 1200(100:100, 100:100, 100:100, 100:100, 100:100, 100:100)

6

Within-center inequality:

W 1 : ntot= 240(10:30, 10:30, 10:30, 10:30, 10:30, 10:30)

W 2 : ntot= 600(25:75, 25:75, 25:75, 25:75, 25:75, 25:75)

W 3 : ntot= 1200(50:150, 50:150, 50:150, 50:150, 50:150, 50:150)

 

Among-centers inequality:

A 1 : ntot= 240(10:10, 10:10, 10:10, 10:10, 10:10, 70:70)

A 2 : ntot= 600(25:25, 25:25, 25:25, 25:25, 25:25, 175:175)

A 3 : ntot= 1200(50:50, 50:50, 50:50, 50:50, 50:50, 350:350)

 

Equal sample size design:

E 1 : ntot= 320(20:20, 20:20, 20:20, 20:20, 20:20, 20:20, 20:20, 20:20)

E 2 : ntot= 800(50:50, 50:50, 50:50, 50:50, 50:50, 50:50, 50:50, 50:50)

E 3 : ntot= 1600(100:100, 100:100, 100:100, 100:100, 100:100, 100:100, 100:100, 100:100)

8

Within-center inequality:

W 1 : ntot= 320(10:30, 10:30, 10:30, 10:30, 10:30, 10:30, 10:30, 10:30)

W 2 : ntot= 800(25:75, 25:75, 25:75, 25:75, 25:75, 25:75, 25:75, 25:75)

W 3 : ntot= 1600(50:150, 50:150, 50:150, 50:150, 50:150, 50:150, 50:150, 50:150)

 

Among-centers inequality:

A 1 : ntot= 320(10:10, 10:10, 10:10, 10:10, 10:10, 10:10, 10:10, 90:90)

A 2 : ntot= 800(25:25, 25:25, 25:25, 25:25, 25:25, 25:25, 25:25, 225:225)

A 3 : ntot= 1600(50:50, 50:50, 50:50, 50:50, 50:50, 50:50, 50:50, 450:450)

  1. Note: In the notation of Ei: Wi: and Ai: ntot= n (n11: n21, ..., n1k: n2k): : is the total number of observations and n k is the number of observations per center.
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BMC Medical Research Methodology

ISSN: 1471-2288

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