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. Author manuscript; available in PMC: 2010 Nov 1.
Published in final edited form as: Osteoporos Int. 2009 Mar 25;20(11):1921–1927. doi: 10.1007/s00198-009-0900-7

Table 3.

The Number of Persons Needed to Adequately Power a Group Randomized Trial of Osteoporosis Treatment Depends on the Magnitude of Clustering

Intra-Class Correlation Coefficient
Hypothesized Proportion
of Patients Treated in an
Intervention Group		 0.00
(i.e. no
clustering)		 0.01 0.03 0.06 0.09
30% 2504 2610 2810 3110 3410
35% 656 690 740 820 900
45% 176 190 200 220 240

Data shown are the number of persons that need to be recruited in order to detect a significant difference with 80% power between the hypothesized intervention group treatment rate and a 25% control group treatment rate, mean cluster size = 5. For simplification, one level of clustering is assumed. Calculations are from reference (12).