J.P.T. Higgins's research while affiliated with University of Bristol and other places
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Publications (31)
Flaws in the conduct of randomized trials can lead to biased estimation of the intervention effect. Methods for adjustment of within‐trial biases in meta‐analysis include the use of empirical evidence from an external collection of meta‐analyses, and the use of expert opinion informed by the assessment of detailed trial information. Our aim is to p...
This is a protocol for a Cochrane Review (Prognosis). The objectives are as follows: Primary objective The primary objective of this review is to determine which technique (test) for assessing MGMT methylation status best predicts overall survival in people diagnosed with glioblastoma who are treated with temozolomide. We will consider each MGMT te...
A key early step in analysing results of studies of effectiveness is identifying the data type for the outcome measurements. This chapter considers outcome data of five common types: dichotomous (or binary) data, continuous data, ordinal data, count or rate data and time-to-event data. The ways in which the effect of an intervention can be assessed...
Planning for the ‘Summary of findings’ table starts early in the systematic review, with the selection of the outcomes to be included in: the review; and the ‘Summary of findings’ table. This is a crucial step, and one that review authors need to address carefully. To ensure production of optimally useful information, Cochrane Reviews begin by deve...
Bias can arise because of the actions of primary study investigators or because of the actions of review authors, or may be unavoidable due to constraints on how research can be undertaken in practice. Where possible, assessments of risk of bias in a systematic review should be informed by evidence. This chapter summarizes some of the key evidence...
Systematic reviews seek to identify all research that meets the eligibility criteria. However, this goal can be compromised by ʼnon-reporting bias’. The convincing evidence for the presence of non-reporting biases should be of great concern to review authors. Regardless of whether an entire study report or a particular study result is unavailable se...
This chapter describes approaches that should be used in systematic reviews for collecting data, including extraction of data directly from journal articles and other reports of studies. The data collected for a review should adequately describe the included studies, support the construction of tables and figures, facilitate the risk of bias assess...
This chapter describes the principles and methods used to carry out a meta-analysis for a comparison of two interventions for the main types of data encountered. A very common and simple version of the meta-analysis procedure is commonly referred to as the inverse-variance method. This approach is implemented in its most basic form in RevMan, and i...
This chapter details version 2 of the Cochrane risk-of-bias tool for randomized trials (RoB 2), the recommended tool for use in Cochrane Reviews. The RoB 2 tool is structured into domains through which bias might be introduced into the result. The chapter summarizes the main features of RoB 2 applied to individually randomized parallel-group trials...
Cochrane Reviews often include non-randomized studies of interventions (NRSI). The Risk Of Bias In Non-randomized Studies of Interventions (ROBINS-I) tool is recommended for assessing risk of bias in a NRSI. This chapter summarizes the biases that can affect NRSI and describes the main features of the ROBINS-I tool. There is greater potential for b...
This chapter addresses first one of the key aspects of interpreting findings that is also fundamental in completing a ‘Summary of findings’ table: the certainty of evidence related to each of the outcomes. It then provides a more detailed consideration of issues around applicability and around interpretation of numerical results, and provides sugge...
This chapter aims to support review authors who are considering including non-randomized studies of interventions (NRSI) in a Cochrane Review. NRSI are defined here as any quantitative study estimating the effectiveness of an intervention (harm or benefit) that does not use randomization to allocate units (individuals or clusters of individuals) to...
Data S1. WinBUGS code for label‐invariant models
Meta-analyses that simultaneously compare multiple treatments (usually referred to as network meta-analyses or mixed treatment comparisons) are becoming increasingly common. An important component of a network meta-analysis is an assessment of the extent to which different sources of evidence are compatible, both substantively and statistically. A...
There is good empirical evidence that specific flaws in the conduct of randomized controlled trials are associated with exaggeration of treatment effect estimates. Mixed treatment comparison meta-analysis, which combines data from trials on several treatments that form a network of comparisons, has the potential both to estimate bias parameters wit...
How can policy makers decide which of five treatments is the best? Standard meta-analysis provides little help but evidence based decisions are possible
Several possible treatments are often available to treat patients with the same condition. Decisions about optimal care, and the clinical practice guidelines that inform these decisions, rely on...
This article shows that the interpretation of the random-effects models used in meta-analysis to summarize heterogeneous treatment effects can have a marked effect on the results from decision models. Sources of variation in meta-analysis include the following: random variation in outcome definition (amounting to a form of measurement error), varia...
Background:
Topical fluorides in the form of toothpaste, mouthrinse, varnish and gel are effective caries preventive measures. However, there is uncertainty about the relative value of these interventions.
Objectives:
To compare the effectiveness of one form of topical fluoride intervention with another when used for the prevention of dental car...
Topical fluoride therapy (TFT) in the form of toothpastes, mouthrinses, varnishes and gels are effective caries preventive measures. However, there is uncertainty about the relative value of these interventions when used together.
To compare the effectiveness of two TFT modalities combined with one of them alone (mainly toothpaste) when used for th...
Background:
Fluoride mouthrinses have been used extensively as a caries-preventive intervention in school-based programmes and individually at home.
Objectives:
To determine the effectiveness and safety of fluoride mouthrinses in the prevention of dental caries in children and to examine factors potentially modifying their effect.
Search strate...
The use of fluoride toothpastes, mouthrinses, gels or varnishes reduces tooth decay in children and adolescents. Tooth decay (dental caries) is painful, expensive to treat and can seriously damage teeth. Fluoride is a mineral that prevents tooth decay. The review of trials found that children aged 5 to 16 years who applied fluoride in the form of t...
Alzheimer's disease sufferers have been found to have a lack of the enzyme responsible for converting choline into acetylcholine within the brain. Lecithin is a major dietary source of choline, so extra consumption may reduce the progression of dementia.
To determine the efficacy of lecithin in the treatment of dementia or cognitive impairment.
The...
Citations
... We assessed the risk of bias in the included studies by using the Prediction Study Risk of Bias Assessment Tool (PROBAST) for RAM studies [10] and the Quality in Prognosis Studies tool (QUIPS) for prognostic factor studies [11][12][13]. ...
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... For KQ1, we also incorporated a sensitivity analysis by calculating absolute effects using an assumed risk based on the general population in Canada (45 to 54 years and ≥65 years) [15,71]. If statistically significant, we calculated the number needed to screen for an additional beneficial outcome (NNS), number needed to treat for an additional beneficial outcome (NNT), or number needed to treat for an additional harmful outcome (NNH) [72]. ...
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... Two authors (REG and RRC) independently assessed the risk of bias of the included studies using Cochrane's "Risk of bias" tool, which is described in Chapter 8 of the Cochrane Handbook for Systematic Reviews of Interventions [28]. Random sequence generation, allocation concealment, blinding of participants and personnel, blinding of outcome assessment, incomplete outcome data, selective reporting, and any other source of bias were all considered. ...
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... This tool was chosen as it was specifically designed for non-randomised interventional studies, which aligns well with the subset of included studies in this review. Additionally, it is endorsed by the Cochrane Handbook for systematic reviews (Sterne et al. 2021). ROBINS-I assesses several domains, including -Confounding bias due to differences in baseline characteristics; selection bias emanating from differences in participants between study groups; classification bias due to misclassifying participants based on intervention status; deviation bias when study participants deviate from intended interventions and outcome bias arising from differences in the methods used to measure outcomes between participants (Sterne et al. 2016). ...
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... According to the Synthesis Without Meta-analysis (SWiM) reporting guidelines, it is recommended to assess the certainty of narrative synthesis findings [29]. To this end, the Grading of Recommendations, Assessment, Development, and Evaluations (GRADE) framework was applied [30]. The studies were grouped by exercise intervention type (strengthening, endurance, and functional exercise). ...
... The impact of study heterogeneity was assessed using the I 2 statistics, with values of < 25%, 25-75%, and > 75% representing low, moderate, and high levels of heterogeneity, respectively [70]. The risk of publication bias was explored for continuous variables (≥ 10 studies per outcome) [71][72][73] using the extended Egger's test [73]. ...
... If studies did not report any essential information, such as mean score, SDs or sample size, the corresponding author was contacted by email. If no reply was obtained, data were extracted from the article's graphs with the WebPlotDigitizer [32], as recommended elsewhere [33]. Moreover, for within-subject studies, such as crossover trials, we considered only data from the first phase to avoid carry-over effects. ...
... Heterogeneity was assessed using the x 2 statistic, but due to the relatively small number of studies and differences across populations and interventions per comparison, we also used the I 2 statistic (reporting the percentage of variability in the effect estimate due to heterogeneity). We followed assumptions that < 40% indicates heterogeneity that may not be important, whilst > 75% indicates considerable heterogeneity (Deeks et al., 2019). To explore heterogeneity, we conducted subgroup analyses. ...
... The direction of the effects (learning outcomes and learning experiences) was used as the standardized metric as there was a lack of precision, which was specific to the effects of the intervention (IVR teaching) and control on the results presented by different studies. This did not allow for the calculation of summary statistics [22]. In addition, the clinical and methodological characteristics (such as populations, intervention components, and the choice of outcome measurements and study designs) of each study were used to evaluate the heterogeneity based on the Cochrane Handbook for Systematic Reviews of Interventions [23]. ...
... If bias is present in primary studies, their results will be incorrect. Subsequently, if a systematic review is based on incorrect evidence, the results of the quantitative analysis will also be incorrect (Boutron et al., 2022;Rytwinski et al., 2021 Drawing from issues we encountered during quantitative synthesis and common features of studies in our evidence base, we recommend the following best practices for improving future study designs and reporting. ...
