Systematic reviews are powerful tools to minimise bias because they use explicit methods. In assessing an intervention for skin disease, the pre-published protocols provide an opportunity to state which participants should ideally be studied, which comparators are appropriate, and which outcomes would make a difference clinically. This "bottom up" and non-reductionist approach also provides the opportunity of consulting consumers (people with a condition or their carers) to ensure that the outcome measures capture something that is important to them. The beneficial role of such consumer involvement was extolled in Chapter 3. Such a pre-planned protocol helps to avoid the problem of being driven by the data already out there and thereby amplifying outcomes that may interest the pharmaceutical industry more than patients and doctors. Even for rare skin diseases, producing a systematic review which finds no reliable evidence to inform practice may still be useful in that one is not missing some important new development, and also highlights the area as a possible research gap for future study.9-11
The basic unit of analysis in most systematic reviews is the RCT. As pointed out in Chapter 9, like any study design, this can be done badly and used in the wrong situations.12 Nevertheless, the RCT remains one of the strongest designs in modern medicine for assessing treatment efficacy because of its potential to minimise bias. As Bigby points out in his essay on "snake oil for the 21st century", studies of inferior design, such as case series, have many times led to overly optimistic claims of treatment efficacy in dermatology which were not borne out by subsequent RCTs.13
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