Rationale, design and conduct of a comprehensive evaluation of a school-based peer-led anti-smoking intervention in the UK: the ASSIST cluster randomised trial [ISRCTN55572965]
1 Department of Social Medicine, University of Bristol, Bristol, UK
2 Cardiff Institute of Society, Health and Ethics, Cardiff University, Cardiff, UK
3 Faculty of Social Sciences, University of Glasgow, Glasgow, UK
BMC Public Health 2007, 7:301 doi:10.1186/1471-2458-7-301Published: 23 October 2007
First paragraph (this article has no abstract)
In preparing the main results paper from this trial, we have noticed an important error in the study protocol paper. In the paragraph headed 'Outcome measures and sample size calculations', the current text "A secondary outcome measure is smoking prevalence among the entire year group." is incorrect, since smoking prevalence among the entire year group is one of two primary outcomes, rather than a secondary outcome. The equal status of the two primary outcomes was agreed at a meeting of the Trial Steering Committee on the 21st January 2005, where the analysis plan was finalised prior to completion of trial data collection. As indicated in the sample size paragraph, study power was considered in terms of both the whole year group and the high-risk sub-group. The incorrect emphasis in the published study protocol paper on the high risk sub-group analysis was a legacy of the funding proposal protocol, in which the sub-group sample size calculations critically determined the number of schools required for the trial.