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Table 2 Minimal effect size that can be detected for the revised sample size given comparison arm risk behaviour prevalence, for a range of ICCs*

From: The prevention access and risk taking in young people (PARTY) project protocol: A cluster randomised controlled trial of health risk screening and motivational interviewing for young people presenting to general practice

  

Effect size

Risk behaviours

Control[7]

ICC = 0.01

ICC = 0.04

ICC = 0.07

Alcohol use

41%

11%

13%

15%

Substance abuse

38%

11%

13%

15%

Tobacco use

24%

9%

10%

12%

  1. ICC = Intracluster Correlation Coefficient; Control = comparison arm.
  2. *Calculations assume an 80% power with alpha of 5% for a two-sided test.
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BMC Public Health

ISSN: 1471-2458

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