Experimental studies rely on the detection of the effects on an intervention. The design is a special application of the case-control study where the exposure is planned and the design prospective. The assumption is that random allocation of subjects to the active intervention or the placebo arms of a study will provide a balanced design, with potential confounders arising by chance with about equal frequency in the study arms. An experimental study is the preferred means of hypothesis testing in most laboratory settings, and relevant methods are subject to continuing improvements (Murray et al., 2004). In human nutrition, the experimental study is most often a randomized, placebo-controlled trial of the possible benefits of dietary manipulation or supplementation. There are numerous good accounts of experimental designs suitable for testing intervention hypotheses in old people; most frequent concerns arise over sample size and statistical power in studies with old people. Latterly, there are many informative commentaries on the quality and generalizability of clinical trial data (e.g., Khaw et al., 2004) that address the recurring problem of the failure of apparent benefits observed in a clinical trial to translate into clinical practice. In nutritional gerontology there are several age-specific problems, not least that dropout rates may be much higher than in younger samples, and sample size calculations need to be set conservatively (Lazovitch et al., 2002).
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