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NSW Public Health Bulletin archive

Sample size calculations for the design of health studies: a review of key concepts for non-statisticians Volume 23 Issue 7-8

Alistair Merrifield, Wayne Smith

NSW Public Health Bulletin 23(8) 142-147 Published: 21 September 2012

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About the author/s

Alistair Merrifield | Centre for Epidemiology and Evidence, NSW Ministry of Health

Wayne Smith | Environmental Health Branch, NSW Ministry of Health

Corresponding author

Alistair Merrifield | [email protected]


Sample size calculations before conducting a health study or clinical trial are important to provide evidence that the proposed study is capable of detecting real associations between study factors. This review aims to clarify statistical issues related to the calculation of sample sizes and is illustrated with an example of a recent study design to improve health outcomes related to water and sewage in NSW Aboriginal communities. The effect of power, significance level and effect size on sample size are discussed. Calculations of sample sizes for individual-based studies are modified for more complex trial designs by multiplying individual-based estimates by an inflationary factor.