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      How to get started with a systematic review in epidemiology: an introductory guide for early career researchers

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          Abstract

          Background

          Systematic review is a powerful research tool which aims to identify and synthesize all evidence relevant to a research question. The approach taken is much like that used in a scientific experiment, with high priority given to the transparency and reproducibility of the methods used and to handling all evidence in a consistent manner.

          Early career researchers may find themselves in a position where they decide to undertake a systematic review, for example it may form part or all of a PhD thesis. Those with no prior experience of systematic review may need considerable support and direction getting started with such a project. Here we set out in simple terms how to get started with a systematic review.

          Discussion

          Advice is given on matters such as developing a review protocol, searching using databases and other methods, data extraction, risk of bias assessment and data synthesis including meta-analysis. Signposts to further information and useful resources are also given.

          Conclusion

          A well-conducted systematic review benefits the scientific field by providing a summary of existing evidence and highlighting unanswered questions. For the individual, undertaking a systematic review is also a great opportunity to improve skills in critical appraisal and in synthesising evidence.

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          Most cited references7

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          Male circumcision and risk of HIV infection in sub-Saharan Africa: a systematic review and meta-analysis.

          To systematically review studies of male circumcision and the risk of HIV-1 infection in men in sub-Saharan Africa, and to summarize the findings in a meta-analysis. A meta-analysis of observational studies. A systematic literature review was carried out of studies published up to April 1999 that included circumcision as a risk factor for HIV-1 infection among men in sub-Saharan Africa. A random effects meta-analysis was used to calculate a pooled relative risk (RR) and 95% confidence interval (CI) for all studies combined, and stratified by type of study population. Further analyses were conducted among those studies that adjusted for potential confounding factors. Twenty-seven studies were included. Of these, 21 showed a reduced risk of HIV among circumcised men, being approximately half that in uncircumcised men (crude RR = 0.52, CI 0.40-0.68). In 15 studies that adjusted for potential confounding factors, the association was even stronger (adjusted RR = 0.42, CI 0.34-0.54). The association was stronger among men at high risk of HIV (crude RR = 0.27; adjusted RR = 0.29, CI 0.20-0.41) than among men in general populations (crude RR = 0.93; adjusted RR = 0.56, CI 0.44-0.70). Male circumcision is associated with a significantly reduced risk of HIV infection among men in sub-Saharan Africa, particularly those at high risk of HIV. These results suggest that consideration should be given to the acceptability and feasibility of providing safe services for male circumcision as an additional HIV prevention strategy in areas of Africa where men are not traditionally circumcised.
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            Bias modelling in evidence synthesis

            Policy decisions often require synthesis of evidence from multiple sources, and the source studies typically vary in rigour and in relevance to the target question. We present simple methods of allowing for differences in rigour (or lack of internal bias) and relevance (or lack of external bias) in evidence synthesis. The methods are developed in the context of reanalysing a UK National Institute for Clinical Excellence technology appraisal in antenatal care, which includes eight comparative studies. Many were historically controlled, only one was a randomized trial and doses, populations and outcomes varied between studies and differed from the target UK setting. Using elicited opinion, we construct prior distributions to represent the biases in each study and perform a bias-adjusted meta-analysis. Adjustment had the effect of shifting the combined estimate away from the null by approximately 10%, and the variance of the combined estimate was almost tripled. Our generic bias modelling approach allows decisions to be based on all available evidence, with less rigorous or less relevant studies downweighted by using computationally simple methods.
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              Development of the RTI item bank on risk of bias and precision of observational studies.

              To create a practical and validated item bank for evaluating the risk of bias and precision of observational studies of interventions or exposures included in systematic evidence reviews. The item bank, developed at RTI International, was created based on 1,492 questions included in earlier instruments, organized by the quality domains identified by Deeks et al. Items were eliminated and refined through face validity, cognitive, content validity, and interrater reliability testing. The resulting item bank consisting of 29 questions for evaluating the risk of bias and precision of observational studies of interventions or exposures (1) captures all of the domains critical for evaluating this type of research, (2) is comprehensive and can be easily lifted "off the shelf" by different researchers, (3) can be adapted to different topic areas and study types (e.g., cohort, case-control, cross-sectional, and case series studies), and (4) provides sufficient instruction to apply the tool to varied topics. One bank of items, with specific instructions for focusing abstractor evaluations, can be created to judge the risk of bias and precision of the variety of observational studies that may be used in systematic and comparative effectiveness reviews. Copyright © 2012 Elsevier Inc. All rights reserved.
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                Author and article information

                Contributors
                Journal
                Arch Public Health
                Arch Public Health
                Archives of Public Health
                BioMed Central
                0778-7367
                2049-3258
                2013
                7 August 2013
                : 71
                : 1
                : 21
                Affiliations
                [1 ]MRC Lifecourse Epidemiology Unit, University of Southampton, Southampton, UK
                [2 ]Academic Geriatric Medicine, University of Southampton, Southampton, UK
                [3 ]MRC Unit for Lifelong Health and Ageing, University College London, London, UK
                Article
                0778-7367-71-21
                10.1186/0778-7367-71-21
                3844862
                23919540
                77bfd865-cf50-4254-9239-a7ea7f83e9b9
                Copyright © 2013 Denison et al.; licensee BioMed Central Ltd.

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 5 July 2013
                : 25 July 2013
                Categories
                Methodology

                Public health
                systematic review,systematic review methods,meta-analysis,early career researchers,evidence synthesis,observational studies

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