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Table 1 Sample size for three test scenarios for primary outcome: hours spent sunbathing per week

From: Design and methods for a cluster randomized trial of the Sunless Study: A skin cancer prevention intervention promoting sunless tanning among beach visitors

  Mean (SD)         
Test Scenarios Control Post-Intervention Expected difference in mean Within-subject correlation No. of cluster (day) Subject/cluster Intra-cluster correlation Minimum size/group Dropout rate Adjusted minimum total size
A (0–2 month) 2.10 (2.0) 1.35 (2.0) 0.75 0.50 16 12 0.01 94 0.15 222
B (0–12 month) 2.10 (2.0) 1.40 (2.0) 0.70 0.50 16 14 0.01 118 0.25 314
C (0–2–12 month) 2.10 (2.0) 1.38 (2.0) 0.72 0.50 16 9 0.01 66 0.25 176