TABLE 2. HIERARCHY OF RESEARCH EVIDENCE Description

Rank 1

Methodology

Systematic review,

meta-analysis 2

Randomised controlled trials (RCT)

3 Cohort study

Systematic review: review of a body of data that uses explicit methods to locate primary studies, and explicit criteria to assess their quality. Meta-analysis: systematic review that uses statistical methods to combine data, and analyse and summarise the results of the studies included.

Experiment in which individuals are randomly allocated to either a control group or a group that receives a specific intervention. Randomisation reduces the likelihood of bias. The strength of evidence is considerably boosted by the presence of at least one properly designed RCT of appropriate size.

Evidence from well-designed trials without randomisation. Cohort study: observational study in which a defined group of people (the cohort) is followed over time. The people are selected on the basis of their exposure to a particular agent and followed up later for specific outcomes.

4

Case-control studies

5

6 7 8

Cross-sectional survey

Case-report Expert opinion

Anecdotal

Evidence from well designed trials without randomisation. Case–control study: study that compares people in two groups with and without a specific condition or disease, all taken from the same population. Usually analysed retrospectively.

Survey or interview of a sample of the population to measure the distribution of interest at a particular point in time.

A report based on a single patient or subject.

Consensus of experience and opinions from respected authorities, based on clinical evidence, descriptive studies or reports from committees.

Informal account of evidence in the form of an anecdote or hearsay, eg. “My granny says the best treatment is to rub it with onions”. The term “anecdotal evidence” is often used in contrast to “scientific evidence”. Anecdotal evidence focuses on experience rather than more formal scientific evidence.

Adapted from: Greenhalgh (20), Sackett et al. (26), and Cochrane (30)

Sheldon and colleagues suggest that, when designing studies, investigators should consider how and by whom their results will be used (21). The design should be sufficiently robust, the setting sufficiently similar to that in which the results are likely to be implemented, the outcomes relevant, and the study size large enough for the results to convince decision makers of their importance.

Although textbooks play an important

role in providing basic information to learners, the drawback with all books is that they are not current (4). Some concepts described in textbooks can lag behind the empirical evidence by as much as 10 years. This lag is in part attributable to the more prolonged publication cycle for textbooks than for journal articles. In summary, treatment interventions should be chosen from the most relevant, scientifically sound and rigorous evidence currently available. Fortunately, the use of hierarchies of evidence can assist clinicians in this process.

THE HIERARCHY OF RESEARCH EVIDENCE Research evidence comes in many forms and varies considerably in quality. The widespread use of hierarchies of evidence that grade

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research studies according to their quality has helped to raise awareness that some forms of evidence are more trustworthy than others (4). In biomedical science, there is general agreement over the advantages of having a hierarchy of evidence, based on validity, essentially designed to reduce the likelihood of errors. The higher up a methodology is ranked in the hierarchy, the more robust and closer to objective truth it is assumed to be. This is clearly desirable for practising clinicians when considering the effectiveness of evidence.

Within the hierarchy ranking, systematic

reviews of rigorous studies are generally accepted to provide the best evidence on the effectiveness of different strategies to promote the implementation of research findings to support clinical practice (22,23). Systematic reviews use scientific strategies to identify, select and critically appraise relevant research within a particular field, and to collect, analyse and quantify data. A meta-analysis is a systematic review that uses statistical methods to combine data and analyse and summarise the results of the studies included. Traditionally, the randomised controlled

trial (RCT) has been regarded as the most objective method of removing bias and producing comparable groups. The RCT is most likely to

sportEX dynamics 2008;18(Oct):10-13

Source of informal verbal communication

Articles published in peer-reviewed research journals

Example

Cochrane Collaboration