|dc.contributor.author||Robinson, Clare Marie||
|dc.identifier.citation||Robinson, C.M. 2016, Sample size calculations for cluster randomised trials, with a focus on ordinal outcomes. Queen Mary University of London||en_US
A common approach to sample size calculation for cluster randomised trials (CRTs) is to calculate
the sample size assuming individual randomisation and multiply it by an inflation factor, the design
effect. This approach is well established for binary and continuous outcomes, but less so for ordinal.
As the variety in trial design increases alternative or more complex methods are required. There is
currently no single resource that provides a comprehensive summary of methods. This thesis aims
to provide a unique contribution towards the review and development of sample size methods for
CRTs, with a focus on ordinal outcomes.
I provide a comprehensive review of sample size methods for CRTs and summarise the methodological
gaps that remain. Through simulation I evaluate the power performance, under realistic
trial scenarios, of the design effect for ordinal outcomes calculated using a kappa-type intracluster
correlation coefficient (ICC), the ICC on an assumed underlying variable and an ANOVA ICC. I
provide practical guidance for sample size calculation for ordinal outcomes in CRTs.
Simulation results showed when the number of clusters was large the ANOVA and kappa-type estimates
were equivalent, and smaller than the latent variable ICC. Use of the ANOVA ICC in the
design effect produced adequately powered trials and power was marginally reduced under a minor
deviation from the common assumption of proportional odds used in ordered regression.
For outcomes with three to five categories the ANOVA ICC, calculated by assigning numerical
equally spaced scores to the ordinal categories, can be used in the simple design effect to produce
an adequately powered trial. The method assumes an analysis by random effects ordered regression
with proportional odds, a reasonable number of clusters, and clusters of the same size.||en_US
|dc.description.sponsorship||Medical Research Council||en_US
|dc.publisher||Queen Mary University of London||en_US
|dc.title||Sample size calculations for cluster randomised trials, with a focus on ordinal outcomes.||en_US
|dc.rights.holder||The copyright of this thesis rests with the author and no quotation from it or information derived from it may be published without the prior written consent of the author||