Within-patient designs and continuous data

In this context, each patient would be receiving each of the multiple treatments. In the cross-over trial with three treatments this would likely be a three-period, three-treatment design and patients would be randomised to one of the six sequences ABC, ACB, BAC, BCA, CAB or CBA. Although there are again ways of asking a simultaneous question relating to the equality of the three treatment means through an analysis of variance approach this is unlikely to be of particular relevance questions of real interest will concern pairwise comparisons. 

Comments as above for the between-patient designs apply also for the within-patient designs and in many cases the best approach will be to focus on a sequence of pairwise comparisons using the paired t-test. 

In the context of within-patient designs, for example the multi-period crossover, there could however, be some additional considerations. Such designs are frequently used in phase I where sample sizes are small and the gains afforded by the common estimation of standard deviation could well be worthwhile, so we should not by any means dismiss these methods completely. 

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