Overreliance on RCTs

Whilst RCTs may be the most robust study design for minimising bias for conventional evaluation of the effectiveness of interventions for skin diseases, they have their limitations.18 In some circumstances, it may be impossible or unethical to perform an RCT. For example, it is unlikely that mothers will agree to be randomised to breastfeeding or bottle-feeding to see whether either prevents atopic eczema. Similarly, it would be impractical to randomise medical students to one form of education and others to another within the same class, because they would not be blinded to the interventions, and there may be considerable "contamination" of the intervention from one group as students talk together. Just because it is an RCT does not mean that it is a good RCT, and attention to quality is important here rather than just blindly following the concept of the hierarchy of evidence.12 Rare but serious events, which are extremely important when evaluating the pros and cons of a new treatment, are not well characterised in RCTs, but instead require other approaches such as case reports, case-control studies and widescale pharmaceutical surveillance methods, as Naldi points out in Chapter 10. Frequently, there is asymmetry in the way that systematic reviews devote a lot of space to treatment efficacy and less or none to issues such as potentially serious side-effects.19

Also, the concept of only using RCTs as evidence for systematic reviews has been criticised because it implies that all other evidence that contributes to our understanding of treatment efficacy, such as case series, case reports and "clinical experience", are not valid.20 This is clearly inappropriate. Ideally, the totality of evidence should be considered when conducting a systematic review so that evidence from observational studies can contribute to the conclusions from RCTs. Approaches such as hierarchical modelling, likelihood estimations and bayesian statistics have been used in attempts to address these gaps. It is likely that the concept of good informative study design is more of a continuum representing risk of bias, rather than a dichotomy of "good" (i.e. RCTs) and "bad" (for example, a large case series). This continuum needs to be tempered by the added but crucial dimension of study quality.

It is true that there are challenges for future systematic reviewers to find ways of incorporating informative data from non-randomised studies, and a methodology group has been set up within the Cochrane Collaboration specifically to address this (http://www.cochrane.dk/nrsmg). In the meantime, it is best that we learn to walk before we run by adhering to the RCT as the basic building block for assessing treatment efficacy in dermatology, at least until better methodological approaches have evolved that enable us to integrate evidence from a wider range of designs.

It should be remembered that EBD is not just based on judging the effectiveness of treatments, even though this is the emphasis in this book. Often, dermatologists want to know "What is the best diagnostic test?", or "What is the prognosis?" or "What is the most cost-effective treatment?". These questions are best addressed using other study designs such as comparison of tests with reference standards in appropriate populations, cohort studies for disease prognosis, and economic studies.1 Some of these are discussed in more detail in Chapters 10 and 11, and more will be added to future editions of the book.

Figure 54.4 A recent Cochrane systematic review found no good evidence to support the use of antistreptococcal interventions (prolonged antibiotics or tonsillectomy) for treating guttate psoriasis. Sometimes such a "negative" systematic review can be useful by empowering patients to question doctors on the evidential basis for their treatment decisions

Figure 54.4 A recent Cochrane systematic review found no good evidence to support the use of antistreptococcal interventions (prolonged antibiotics or tonsillectomy) for treating guttate psoriasis. Sometimes such a "negative" systematic review can be useful by empowering patients to question doctors on the evidential basis for their treatment decisions

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