At the SR Core, we are conversant with methodological standards and processes for systematic and other reviews, and our goal is to help you develop a high-quality manuscript following sound methdology (National Institutes of Medicine, Cochrane Handbook, Agency for Healthcare Research and Quality, Joanna Briggs Institute, OHAT) and reporting guidelines (PRISMA, MOOSE).
SR Core Services
- Question refinement
- Finding the right fit between your objectives and type of review
- Methodological guidance on all aspects of systematic (and other) reviewing
- Protocol Development:
- Inclusion & Exclusion Criteria
- Search methods and search process
- Data extraction—elements and process
- Statistical analysis plan (in consultation with statisticians from the Study Design and Biostatistics Center (SDBC)
- search methodology
- background information
- search plan and methodology to inform IRB applications and grants.
- Bibliographic data management
- Systematic Review Software—advice on choice and set up
- Full text retrieval of journal articles
- Identifying relevant journals for publication
Are the best known, but not the only, type of evidence synthesis. The objective of a systematic review is to find, appraise and synthesize evidence while minimizing bias by following an a priori plan that is reproducible. Systematic reviews typically seek to answer a specific question about ‘what works’ or ‘which (intervention) is best’ by synthesizing data from randomized or controlled trials (RCTs); but methods to incorporate observations studies are available.
Other types of evidence synthesis incorporate aspects of the systematic review process, but differ as follows:
Includes a sensitive literature search, but its goal is to provide an overview of a field versus answering a specific question. Will frequently include many types of studies and literature, not just controlled or randomized trials.
May employ a less sensitive literature search, may not assess risk of bias, or may employ date limits in an effort to respond to a question in a more timely manner than a Systematic Review.
Seeks to determine why and how an intervention or group of interventions or processes work and in what circumstances. Will examine and incorporate theoretical frameworks to inform understanding of the how and why.
Overview of Reviews
Will synthesize data from multiple systematic reviews with something in common, such as a disease (e.g an overview of systematic reviews on diabetes may synthesize evidence of both pharmacological and non-pharmacological interventions to improve management of blood glucose levels).
Meta-analysis associated with Systematic Reviews of Randomized Controlled Trials, and is defined in the Cochrane Handbook as the “statistical combination of results from two or more separate studies.” Following are key points to consider when developing a data synthesis plan for a Cochrane (or other) systematic review:
- Potential advantages of meta-analyses include an increase in power, an improvement in precision, the ability to answer questions not posed by individual studies, and the opportunity to settle controversies arising from conflicting claims. However, they also have the potential to mislead seriously, particularly if specific study designs, within-study biases, variation across studies, and reporting biases are not carefully considered.
- It is important to be familiar with the type of data (e.g. dichotomous, continuous) that result from measurement of an outcome in an individual study, and to choose suitable effect measures for comparing intervention groups.
- Most meta-analysis methods are variations on a weighted average of the effect estimates from the different studies.
- Variation across studies (heterogeneity) must be considered, although most Cochrane reviews do not have enough studies to allow the reliable investigation of the reasons for it. Random-effects meta-analyses allow for heterogeneity by assuming that underlying effects follow a normal distribution.
- Many judgements are required in the process of preparing a Cochrane review or meta-analysis. Sensitivity analyses should be used to examine whether overall findings are robust to potentially influential decisions.
Incorporating data from non-randomized studies
- See Chapter 13.6.1 of the Cochrane Handbook
- “Network meta-analysis, in the context of a systematic review, is a meta-analysis in which multiple treatments (that is, three or more) are being compared using both direct comparisons of interventions within randomized controlled trials and indirect comparisons across trials based on a common comparator.” Li et al. BMC Medicine 20119:79