Finding evidence and advances in the organization of clinical knowledge

Identification of the nature of the clinical question and the most reliable study design enables the clinician to perform a focused and efficient literature search. One of the main advances of evidence-based medicine has been the development of methods of research synthesis, or the process of identifying, appraising, and summarizing primary research studies into clinically usable knowledge. There are currently two main approaches to research synthesis—systematic reviews and clinical practice guidelines. Both these approaches are based on an explicit methodology that begins with the construction of a hierarchy of evidence in which certain forms of research architecture are considered to be reliable than others. The methodology is most clearly developed for questions about therapy and these will be the focus here.

Levels of evidence

A commonly used hierarchy of evidence for studies of treatments is as follows.

Ia. Evidence from a systematic review of randomized controlled trials Ib. Evidence from at least one randomized controlled trial IIa.Evidence from at least one controlled study without randomization IIb.Evidence from at least one other type of quasi-experimental study

III. Evidence from non-experimental descriptive studies, such as comparative studies, correlation studies, and case-control studies

IV. Evidence from expert committee reports or opinions and/or clinical experience of respected authorities.

In this hierarchy, randomized evidence is considered to be more reliable than non-randomized evidence, and a systematic review of randomized evidence is considered to be the best defence against systematic bias.

Hierarchies of evidence have also been formulated for non-therapeutic studies, such as studies of aetiology, diagnosis, and prognosis. Again, the fundamental feature of these hierarchies is that the study architectures with the least susceptibility to bias are considered most reliable. The study design considered most reliable for each type of clinical question is shown in Table l.

Systematic reviews

The need for systematic reviews and the methodology used are described in Chapter. The recognition of the need for systematic reviews of randomized controlled trials, and the development of the scientific methodology of reviews, has been one of the most striking advances in health services research over the last decade. One key development was the founding of the Cochrane Collaboration, an international organization with the objective of producing regularly updated systematic reviews of the effectiveness of all health care interventions. (.12> The first Cochrane Centre was established in Oxford in 1992 as part of the information systems strategy developed to support the National Health Service Research and Development Programme; centres have since been established in several other countries.

Clinical practice guidelines

In some areas of health care there is sufficient evidence, coexisting with substantial clinical uncertainty, that it is worth developing clinical practice guidelines. Clinical practice guidelines have been defined as 'systematically developed statements to assist practitioner decisions about appropriate health care for specific clinical circumstances'.'13) Guidelines have been developed for several years, but there have been recent advances in the methodology of producing explicitly evidence-based guidelines. Evidence-based clinical practice guidelines are developed by a guideline development group consisting of key stakeholders who decide on the precise clinical questions to be answered. The evidence is then systematically reviewed and classified according to a hierarchy of evidence (see above) and presented to the guideline development group. The group then makes recommendations as appropriate. The degree to which the recommendations are directly based on the evidence is described using a second level of classification: (14)

1. directly based on category I evidence;

2. directly based on category II evidence or extrapolated recommendation from category I evidence;

3. directly based on category III evidence or extrapolated recommendation from category I or II evidence;

4. directly based on category IV evidence or extrapolated recommendation from category I, II. or III evidence.

Clinical practice guidelines are usually developed at a national level and need tailoring to suit local circumstances. Professional bodies such as the American Psychiatric Association and the Royal College of Psychiatrists (both of which have active guideline development programmes) usually take responsibility for developing national guidelines.

There are several limitations to clinical practice guidelines. Firstly, evidence-based clinical practice guidelines are expensive and time consuming to produce and rapidly become out of date. Secondly, to influence practice, evidence-based clinical practice guidelines need to be actively disseminated and implemented. Guidelines that are developed nationally and passively sent out to doctors are often not used. (15) A number of active approaches are effective in helping change clinicians' behaviour:(16)

• outreach visits (also known as academic detailing)

• local opinion leaders

• patient-mediated interventions (including patient education)

• multifaceted interventions involving a range of techniques.

There is some evidence that guidelines can improve patient outcomes by their effect on clinical practice, especially when they are made relevant to local circumstances.1.* In one study in the United States, 217 patients with depressive disorders were randomly assigned to usual care or a mulitifaceted intervention designed to achieve the Agency for Health Care Policy and Research guidelines on management of depression. (!7) Patients in the intervention group were much more likely to be treated in accordance with the guidelines, and this led to improved outcomes in patients with major depressive disorder (more than 50 per cent reduction on the Symptom Checklist-90 Depressive Symptom Scale at 4 months in 74 per cent of experimental patients compared with 44 per cent of control patients).

Understandably, clinicians also seek guidance in important clinical questions that are poorly served by high-quality, especially randomized, evidence. To assist in these clinical decisions, Frances and his colleagues have developed an innovative method of guideline development based on a systematic survey of the views of clinical experts.(1,19)

Use of electronic communication and the World Wide Web

The development of the Internet during the 1990s is closely linked to the development of evidence-based practice. The World Wide Web has become a vast information resource for doctors and patients. The improved access to information afforded to patients means that they are often very well informed about their condition. This is one of the factors contributing to the need for doctors to improve their own access to information. The Internet has several drawbacks including the disorganization of the information and the lack of quality control.(2 As with paper publications, resources are being developed to index critically appraised websites selectively. An example of such a site containing comprehensive links to useful information on the Web is the Centre for Evidence Based Mental Health (httfi:// Although in its infancy, over the next few years the Web is likely to become the main medium for transmitting and storing knowledge. Reliable electronic resources such as the Cochrane Library are already available ( http:i//www.updatezs9itw§.^[®.:com/c9w®b).

Improving current awareness

Another area of improvement has been the development of tools to assist doctors to maintain their current awareness of advances in research. The idea of review and abstracting journals is not new, but there has been a recognition that such journals also need a methodology to allow them to identify the most reliable and clinically important research studies.

A number of new journals have been produced with the aim improving the availability of high-quality evidence to clinicians. The first of these was ACP Journal Club (targeted primarily at general physicians), followed by Evidence-Based Medicine (targeted primarily at family doctors) and, more recently, Evidence-Based Mental Health (aimed at mental health clinicians of all disciplines). Evidence-Based Mental Health scans over 200 journals regularly and selects only those articles that both meet explicit methodological criteria (see BoxJ) and are clinically important. The articles are then summarized in structured abstracts and published on one page with an accompanying commentary by a clinical expert.

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