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Methods for the thematic synthesis of qualitative research in systematic reviews
Information for What is Systematic Reviewing? Denise E. Bronson and Tamara S. New York, Oxford University Press, Research on Social Work Practice 16 3 , May , pp. Test-tube Lab Research "Test tube" experiments conducted in a controlled laboratory setting. Adapted from Study Designs.
Bias - Any deviation of results or inferences from the truth, or processes leading to such deviation. Bias can result from several sources: one-sided or systematic variations in measurement from the true value systematic error ; flaws in study design; deviation of inferences, interpretations, or analyses based on flawed data or data collection; etc. There is no sense of prejudice or subjectivity implied in the assessment of bias under these conditions.
Case Control Studies - Studies which start with the identification of persons with a disease of interest and a control comparison, referent group without the disease. The relationship of an attribute to the disease is examined by comparing diseased and non-diseased persons with regard to the frequency or levels of the attribute in each group. Causality - The relating of causes to the effects they produce.
Causes are termed necessary when they must always precede an effect and sufficient when they initiate or produce an effect. Any of several factors may be associated with the potential disease causation or outcome, including predisposing factors, enabling factors, precipitating factors, reinforcing factors, and risk factors. Control Groups - Groups that serve as a standard for comparison in experimental studies.
They are similar in relevant characteristics to the experimental group but do not receive the experimental intervention.
Controlled Clinical Trials - Clinical trials involving one or more test treatments, at least one control treatment, specified outcome measures for evaluating the studied intervention, and a bias-free method for assigning patients to the test treatment.
The treatment may be drugs, devices, or procedures studied for diagnostic, therapeutic, or prophylactic effectiveness. Control measures include placebos, active medicines, no-treatment, dosage forms and regimens, historical comparisons, etc. When randomization using mathematical techniques, such as the use of a random numbers table, is employed to assign patients to test or control treatments, the trials are characterized as Randomized Controlled Trials. Cost-Benefit Analysis - A method of comparing the cost of a program with its expected benefits in dollars or other currency. The benefit-to-cost ratio is a measure of total return expected per unit of money spent.
This analysis generally excludes consideration of factors that are not measured ultimately in economic terms. Cost effectiveness compares alternative ways to achieve a specific set of results. Cross-Over Studies - Studies comparing two or more treatments or interventions in which the subjects or patients, upon completion of the course of one treatment, are switched to another. In the case of two treatments, A and B, half the subjects are randomly allocated to receive these in the order A, B and half to receive them in the order B, A.
A criticism of this design is that effects of the first treatment may carry over into the period when the second is given. Cross-Sectional Studies - Studies in which the presence or absence of disease or other health-related variables are determined in each member of the study population or in a representative sample at one particular time. Double-Blind Method - A method of studying a drug or procedure in which both the subjects and investigators are kept unaware of who is actually getting which specific treatment.
Empirical Research - The study, based on direct observation, use of statistical records, interviews, or experimental methods, of actual practices or the actual impact of practices or policies. Evaluation Studies - Works consisting of studies determining the effectiveness or utility of processes, personnel, and equipment. Genome-Wide Association Study - An analysis comparing the allele frequencies of all available or a whole genome representative set of polymorphic markers in unrelated patients with a specific symptom or disease condition, and those of healthy controls to identify markers associated with a specific disease or condition.
Logistic Models - Statistical models which describe the relationship between a qualitative dependent variable that is, one which can take only certain discrete values, such as the presence or absence of a disease and an independent variable. A common application is in epidemiology for estimating an individual's risk probability of a disease as a function of a given risk factor.
Systematic Reviews and Meta-Analysis
Longitudinal Studies - Studies in which variables relating to an individual or group of individuals are assessed over a period of time. Lost to Follow-Up - Study subjects in cohort studies whose outcomes are unknown e.
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Matched-Pair Analysis - A type of analysis in which subjects in a study group and a comparison group are made comparable with respect to extraneous factors by individually pairing study subjects with the comparison group subjects e. Meta-Analysis - Works consisting of studies using a quantitative method of combining the results of independent studies usually drawn from the published literature and synthesizing summaries and conclusions which may be used to evaluate therapeutic effectiveness, plan new studies, etc. Some databases use one or the other method for searching, andin some cases either approach can be used.
Knowing which method is. It is also important to identify a priori the search terms to be used. This starts by breaking the search question into its PICO componentparts and identifying any synonyms the database might use to capturethe key concepts. Initially this task is a bit of a trial-and-error process.
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In addition, databases use 1 truncation or wildcard characters e. For example, Table 2. It illus-trates how the search question was broken down into its componentparts and the numerous terms that were used within each category.
The AND operator is used across the categories of terms to. Typically, publicationbias refers to the fact that articles with negative or unexpected results areless likely to be accepted for publication and published studies are morelikely to conclude that an intervention is effective. However, the term hascome to encompass many other reasons for the systematic exclusion ofrelevant research from a systematic review. Rothstein et al. In medicine, problems with publicationbias have resulted in potential or actual harm to patients Chalmers,; Rennie, ; Simes, ; Sterne, Juni, Schulz, Altman, Bartlett,.
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Any systematic review that relies solely on electronic databases may inadvertently introduce one or more type of publication bias. The result is that the systematic review may overestimate the effec- tiveness of an intervention by systematically excluding some studies with negative or no differences Rothstein et al. Hand Searching of Key Journals: Searching electronic databases will not reveal all of the relevant literature that should be included in a sys- tematic review. Hand searching for studies in key journals is used to supplement the electronic searches and to identify articles that might have been missed.
The hand-searching process involves identifying key journals that are likely to contain relevant studies, setting the range of dates for the journals to be searched, and scanning the table of contents for rele- vant research. Reference Mining from Previous Systematic Reviews: Another strategy for locating relevant research is to review the references of articles that have met the inclusion and exclusion criteria. The same criteria are applied to determine if studies that are cited in a research report are appropriate for the systematic review.
Frequently, older or unpublished studies in the topic area may appear in the reference list. Those that initially meet the inclusion criteria are retrieved and subjected to an abstract and full review as appropriate. Notes should be kept on who was contacted, what references were obtained, and the rationale for contacting that individual.
In This Article
Readers of your systematic review need. As was noted earlier, multiple studies across many disciplines have docu-mented the tendency of journal reviewers and editors to favor articlesthat have positive i. Beyond the role of bias in unpublished research,it may also be that a report written to a funder at the conclusion of anintervention study was never rewritten as a journal article due to a myriadof possible reasons.
To present an accurate picture on theeffectiveness of an intervention it is necessary to include all studies thathave been completed in a particular area rather than relying on onlythose that have been published. Finding the gray literature can present a serious challenge tothose undertaking a systematic review. These processes are somewhat analogous to develop- ing a sound research question and collecting valid and reliable data for a primary research study.
Grayson and Gomersall note: A review may be of impeccable quality in terms of inclusion criteria, data extraction, synthesis of evidence from different research methodologies, and so forth. The next chapter looks at ways to assess i. Bibliographic Databases for Social Care Searching. London: Social Care Institute for Excellence.
Grayson, L. Campbell Systematic Reviews Supplement 1. DOI: Rothstein, H. Including studies of poor quality, low rigor, or questionable credibility is likely to lead to conclusions that are meaningless or, even worse, completely wrong. It is important, therefore, to appraise the quality or value of the research before it is incorporated into a systematic review.
Research varies widely on the rigor of methods used, the context in which the study occurs, and the strength of the conclusions provided.
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Critically appraising the available studies in an area of inquiry helps to determine which provide a fair evaluation of the intervention. Numerous scales and checklists have been developed to assist in appraising research studies. Some approaches focus on assessing threats This chapter focuses on appraising the research in terms of both thequality of its methods as well as potential biases that can reduce thebelievability or credibility of the original research.
Studies are assessed on 1 the quality or internal validity of the research methods, 2 the exter-nal validity and relevance of the research, and 3 the credibility of theresearcher Bronson, A strong research report provides detailed information aboutthe research design, methods used, where the study took place, who par-ticipated, and the intervention s employed. Thus, assessing the qualityof the research depends greatly on the amount of information providedin the article.
The written report of the original research should be trans-parent, thorough, and provide enough detail that the study could be rep-licated. Check for reviewer interrater reliability throughout the retrieval and appraisal process. Have two or more reviewers judge the research on the extent to which it complies with the preestablished inclusion and exclusion criteria, and rate the study on the rigor of the research design and implementation.
If both raters share the same bias then their reliability does not reduce the likelihood that the retrieval and appraisal will be unbiased. Use a standardized approach that applies the same evaluative criteria to appraise all research studies. Taking these precautions prior to critically appraising the research stud- ies increases the credibility and value of the systematic review.
External validity is closely connected to the relevance ofthe study to existing practice and policy problems.