Randomized controlled trials subject variation

Rather, the persons should be randomised to two different treatments, placebo and active treatment one after the other, with a wash-out period between, the randomisation gives the random order of the treatments. By such a design effects e.g. due to season is randomly allocated to the groups. The advantage of the paired design is that each person serves as his own control, and the number of subjects in the trial is reduced compared with the un-paired trial. Among the disadvantages are that every time a person drops out the first measurement he/she cannot be included in the analysis. Furthermore, if the variation within individuals is comparable with that between individuals, extra power is not obtained. 

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