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EXW 500: Cochrane Database

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Cochrane Handbook

Systematic Review Defined

Cochrane Handbook  |   1.2.2  What is a systematic review?

A systematic review attempts to collate all empirical evidence that fits pre-specified eligibility criteria in order to answer a specific research question.  It  uses explicit, systematic methods that are selected with a view to minimizing bias, thus providing more reliable findings from which conclusions can be drawn and decisions made (Antman 1992, Oxman 1993). The key characteristics of a systematic review are:

  • a clearly stated set of objectives with pre-defined eligibility criteria for studies;

  • an explicit, reproducible methodology;

  • a systematic search that attempts to identify all studies that would meet the eligibility criteria;

  • an assessment of the validity of the findings of the included studies, for example through the assessment of risk of bias; and

  • a systematic presentation, and synthesis, of the characteristics and findings of the included studies.

 

Many systematic reviews contain meta-analyses. Meta-analysis is the use of statistical methods to summarize the results of independent studies (Glass 1976). By combining information from all relevant studies, meta-analyses can provide more precise estimates of the effects of health care than those derived from the individual studies included within a review (see Chapter 9, Section 9.1.3). They also facilitate investigations of the consistency of evidence across studies, and the exploration of differences across studies.

 

Searching Cochrane

 

Cochrane Library

The Cochrane Library is a collection of databases that contain high-quality, independent evidence to inform healthcare decision-making. Cochrane Reviews represent the highest level of evidence on which to base clinical treatment decisions. In addition to Cochrane Reviews, The Cochrane Library provides other sources of reliable information: other systematic reviews abstracts, technology assessments, economic evaluations, and individual clinical trials – all the current evidence in one single environment

A systematic review identifies an intervention for a specific disease or other problem in health care, and determines whether or not this intervention works. To do this authors locate, appraise and synthesize evidence from as many relevant scientific studies as possible. They summarize conclusions about effectiveness, and provide a unique collation of the known evidence on a given topic, so that others can easily review the primary studies for any intervention.

 

The Cochrane Central Register of Controlled Trials (CENTRAL) serves as the most comprehensive source of reports of controlled trials. CENTRAL is published as part of The Cochrane Library and is updated quarterly. As of January 2008 (Issue 1, 2008), CENTRAL contains nearly 530,000 citations to reports of trials and other studies potentially eligible for inclusion in Cochrane reviews, of which 310,000 trial reports are from MEDLINE, 50,000 additional trial reports are from EMBASE and the remaining 170,000 are from other sources such as other databases and handsearching.

Search strategies

  •   Avoid too many different search concepts but use a wide variety of synonyms and related terms (both free text and controlled vocabulary terms) combined with ‘OR’ within each concept.

  • Combine different concepts with ‘AND’.

  • The 310,000 records sourced from MEDLINE are best retrieved by a combination of Medical Subject Heading (MeSH) and free-text terms.

  • Cochrane Handbook | Definition of Qualitative Research

     Cochrane Handbook | 20.2.1 Definition of Qualitative Research 

    Qualitative researchers study things in their natural settings, attempting to make sense of, or to interpret, phenomena in terms of the meanings people bring to them (Denzin 1994). Qualitative research is intended to penetrate to the deeper significance that the subject of the research ascribes to the topic being researched. It involves an interpretive, naturalistic approach to its subject matter and gives priority to what the data contribute to important research questions or existing information.

    Within health care an understanding of the value of evidence from qualitative research to systematic reviews must consider the varied and diffuse nature of evidence (Popay 1998b, Pearson 2005). Qualitative research encompasses a range of philosophies, research designs and specific techniques including in-depth qualitative interviews; participant and non-participant observation; focus groups; document analyses; and a number of other methods of data collection (Pope 2006). Given this range of data types, there are also diverse methodological and theoretical approaches to study design and data analysis such as phenomenology; ethnography; grounded theory; action research; case studies; and a number of others. Theory and the researchers’ perspective also play a key role in qualitative data analysis and in the bases on which generalizations to other contexts may be made.

    Within the empirical sciences, the standing of a given theory or hypothesis is entirely dependent upon the quantity and character of the evidence in its favour. It is the relative weight of supporting evidence that allows us to choose between competing theories. Within the natural sciences, knowledge generation involves testing a hypothesis or a set of hypotheses by deriving consequences from it and then testing whether those consequences hold true by experiment and observation.  

    Health professionals seek evidence to substantiate the worth of a very wide range of activities and interventions and thus the type of evidence needed depends on the nature of the activity and its purpose. For many research questions, for example, those about parental beliefs and childhood vaccination (Mills 2005a, Mills 2005b), qualitative research is an appropriate and desirable methodology.

    Cochrane Handbook | 20.2.2  Using evidence from qualitative research in Cochrane reviews

    We identify four ways in which qualitative research can contribute to Cochrane Intervention reviews for health policy and practice (Popay 2006a):

    1. Informing reviews by using evidence from qualitative research to help define and refine the question. This ensures the review includes appropriate studies and addresses important outcomes, allowing the review to be of maximum relevance to potential users.

    2. Enhancing reviews by synthesizing evidence from qualitative research identified whilst looking for evidence of effectiveness. Qualitative evidence associated with trials can be used to explore issues of implementation of the intervention. We consider qualitative research performed alongside randomized trials in more detail in Section 20.2.3.

    3. Extending reviews by undertaking a search and synthesis specifically of evidence from qualitative studies to address questions directly related to the effectiveness review.

    4. Supplementing reviews by synthesizing qualitative evidence to address questions on aspects other than effectiveness.

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