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      The Cochrane Collaboration’s tool for assessing risk of bias in randomised trials

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          Abstract

          Flaws in the design, conduct, analysis, and reporting of randomised trials can cause the effect of an intervention to be underestimated or overestimated. The Cochrane Collaboration’s tool for assessing risk of bias aims to make the process clearer and more accurate

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          Most cited references 15

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          GRADE: an emerging consensus on rating quality of evidence and strength of recommendations.

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            Empirical evidence of bias in treatment effect estimates in controlled trials with different interventions and outcomes: meta-epidemiological study.

            To examine whether the association of inadequate or unclear allocation concealment and lack of blinding with biased estimates of intervention effects varies with the nature of the intervention or outcome. Combined analysis of data from three meta-epidemiological studies based on collections of meta-analyses. 146 meta-analyses including 1346 trials examining a wide range of interventions and outcomes. Ratios of odds ratios quantifying the degree of bias associated with inadequate or unclear allocation concealment, and lack of blinding, for trials with different types of intervention and outcome. A ratio of odds ratios <1 implies that inadequately concealed or non-blinded trials exaggerate intervention effect estimates. In trials with subjective outcomes effect estimates were exaggerated when there was inadequate or unclear allocation concealment (ratio of odds ratios 0.69 (95% CI 0.59 to 0.82)) or lack of blinding (0.75 (0.61 to 0.93)). In contrast, there was little evidence of bias in trials with objective outcomes: ratios of odds ratios 0.91 (0.80 to 1.03) for inadequate or unclear allocation concealment and 1.01 (0.92 to 1.10) for lack of blinding. There was little evidence for a difference between trials of drug and non-drug interventions. Except for trials with all cause mortality as the outcome, the magnitude of bias varied between meta-analyses. The average bias associated with defects in the conduct of randomised trials varies with the type of outcome. Systematic reviewers should routinely assess the risk of bias in the results of trials, and should report meta-analyses restricted to trials at low risk of bias either as the primary analysis or in conjunction with less restrictive analyses.
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              Tamsulosin treatment for benign prostatic hyperplasia and risk of severe hypotension in men aged 40-85 years in the United States: risk window analyses using between and within patient methodology

              Objective To characterize risk of hypotension requiring admission to hospital in middle aged and older men treated with tamsulosin for benign prostatic hyperplasia. Design Population based retrospective cohort study (between patient methodology) and self controlled case series (within patient methodology). Setting Healthcare claims data from the IMS Lifelink database in the United States. Participants Men aged 40-85 years with private US healthcare insurance entering the cohort at their first dispensing for tamsulosin or for a 5α reductase inhibitor (5ARI) between January 2001 and June 2011after a minimum of six months’ enrolment. Main outcomes measures Hypotension requiring admission to hospital. Cox proportional hazards models estimated rate ratios at time varying intervals during follow-up: weeks 1-4, 5-8, and 9-12 after tamsulosin initiation; weeks 1-4, 5-8, and 9-12 after restarting tamsulosin (after a four week gap); and maintenance tamsulosin treatment (remaining exposed person time). Covariates included age, calendar year, demographics, antihypertensive use, healthcare use, and a Charlson comorbidity score. A self controlled case series, having implicit control for time invariant covariates, was additionally conducted. Results Among 383 567 new users of study drugs (tamsulosin 297 596; 5ARI 85 971), 2562 admissions to hospital for severe hypotension were identified. The incidence for hypotension was higher for tamsulosin (42.4 events per 10 000 person years) than for 5ARIs (31.3 events per 10 000 person years) or all accrued person time (29.1 events per 10 000 person years). After tamsulosin initiation, the cohort analysis identified an increased rate of hypotension during weeks 1-4 (rate ratio 2.12 (95% confidence interval 1.29 to 3.04)) and 5-8 (1.51 (1.04 to 2.18)), and no significant increase at weeks 9-12. The rate ratio for hypotension also increased at weeks 1-4 (1.84 (1.46 to 2.33)) and 5-8 (1.85 (1.45 to 2.36)) after restarting tamsulosin, as did maintenance tamsulosin treatment (1.19 (1.07 to 1.32)). The self controlled case series gave similar results as the cohort analysis. Conclusions We observed a temporal association between tamsulosin use for benign prostatic hyperplasia and severe hypotension during the first eight weeks after initiating treatment and the first eight weeks after restarting treatment. This association suggests that physicians should focus on improving counseling strategies to warn patients regarding the “first dose phenomenon” with tamsulosin.
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                Author and article information

                Contributors
                Role: senior statistician
                Role: director
                Role: director
                Role: head of division
                Role: senior scientist
                Role: senior researcher
                Role: postdoctoral fellow
                Role: vice president
                Role: research associate
                Role: professor of medical statistics and epidemiology
                Journal
                BMJ
                bmj
                BMJ : British Medical Journal
                BMJ Publishing Group Ltd.
                0959-8138
                1468-5833
                2011
                2011
                18 October 2011
                : 343
                Affiliations
                [1 ]MRC Biostatistics Unit, Institute of Public Health, Cambridge CB2 0SR, UK
                [2 ]Centre for Statistics in Medicine, University of Oxford, Oxford, UK
                [3 ]The Nordic Cochrane Centre, Rigshospitalet and University of Copenhagen, Denmark
                [4 ]Institute of Social and Preventive Medicine, University of Bern, Switzerland
                [5 ]Clinical Epidemiology Program, Ottawa Hospital Research Institute, Ottawa, Ontario, Canada
                [6 ]Department of Epidemiology and Community Medicine, Faculty of Medicine, University of Ottawa, Canada
                [7 ]Preventive and International Health Care Unit, Norwegian Knowledge Centre for the Health Services, Oslo, Norway
                [8 ]Department of Social Medicine, University of Bristol, Bristol, UK
                [9 ]FHI, Research Triangle Park, North Carolina, USA
                Author notes
                Correspondence to: J P T Higgins julian.higgins@ 123456mrc-bsu.cam.ac.uk .
                Article
                higj860676
                10.1136/bmj.d5928
                3196245
                22008217
                © Higgins et al 2011

                This is an open-access article distributed under the terms of the Creative Commons Attribution Non-commercial License, which permits use, distribution, and reproduction in any medium, provided the original work is properly cited, the use is non commercial and is otherwise in compliance with the license. See: http://creativecommons.org/licenses/by-nc/2.0/ and http://creativecommons.org/licenses/by-nc/2.0/legalcode.

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                Research Methods & Reporting

                Medicine

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