A number of types of clinical investigation are described in this chapter, and elsewhere in the book. When making clinical decisions about a course of therapeutic action, it is obviously relevant to judge the strength of evidence generated by different types of study. This has been summarised as follows, in rank order.38
1. Systematic reviews and meta-analysis
2. Randomised controlled trials with definitive results (confidence intervals that do not overlap the threshold of the clinically significant effect)
3. Randomised controlled trials with nondefinitive results (a difference that suggests a clinically significant effect but with confidence intervals overlapping the threshold of this effect)
4. Cohort studies
5. Case-control studies
6. Cross-sectional surveys
7. Case reports.
38 Guyatt G H et al 1995 Journal of the American Medical Association 274:1800.
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