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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

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BMC Public Health

ISSN: 1471-2458

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