1. Design of cost- effectiveness studies Some introductory remarks by Tony O’Hagan

2. Welcome! Welcome to the fifth CHEBS dissemination workshop This forms part of our Focus Fortnight on “Design and sample size for cost-effectiveness studies” Our format allows plenty of time for discussion of the issues raised in each talk, so please feel free to join in!

3. Trial design Design of clinical trials and other observational studies is an area of research with many facets ›comparators, blinding, sequential/interim, outcome measures, sample size, … One question that is routinely referred for statistical evaluation is that of sample size This is itself a large and complex research topic ›depends on other design facets, distributions of outcomes, objectives, …

4. C-E trials The increasing importance of economic evaluation has led to an emphasis on gathering economic information alongside a conventional efficacy trial Sample size calculations have been devised ›Only assuming joint normality of costs and efficacy But sample size is in practice rarely determined with economic evaluation as the primary objective

5. C-E trials (2) Despite the growing number of such trials, they will rarely provide all the evidence needed for an economic evaluation ›The more realistic context is that they provide evidence on some parameters in an economic model ›Given that other information must be sought from outside the trial anyway, why bother to get economic data in the trial?

6. Challenges Sample size calculations with more realistic modelling of ›data ›decision problem Accepting that sample size will actually be chosen on other criteria Quantifying the extra value of ›resource use data ›more pragmatic trials