Systematic Reviews

Comprehensive Literature Searching

Databases must be searched as comprehensively as possible in order to identify all of the documents relevant to your systematic review. These five components are typically used when searching:

• Controlled vocabulary (e.g., PubMed's MeSH, Embase's Emtree, etc.)
• Keywords
• Boolean operators (AND, OR, NOT) and proximity operators
• Database specific syntax that allows for searching of phrases, parts of a document, variant of terms, etc.

Using Literature Databases

When searching for health and medical information, it's usually recommended to search a MEDLINE database (ex: PubMed), Embase, and Cochrane Library. All are available at UNMC.

Always check for requirements or recommendations specific to guidelines for the type of review you are conducting. Things to consider when choosing your databases/resources:

• Subject area
• Regional coverage
• Language coverage

Grey Literature

Grey literature is information produced by government agencies, academic institutions, and for-profit section that is not available by commercial publishers. This kind of literature may contain unique and relevant evidence related to your review.

Examples:

• Clinical Trials
• Reports
• Proceedings
• Dissertations and thesis
• White papers, newsletters, and patents.

Screening Studies

The selection of studies is a two-step process that includes a title/abstract review followed by a full text review. Studies are reviewed according to the pre-established inclusion/exclusion criteria by (at least) two reviewers, who must agree to include or exclude. Any conflicts are resolved by a third reviewer.

Screening Tools

Study Appraisal

Study appraisal systematically examines factors such as:

• The appropriateness of study design
• Outcome measures
• Methodological quality and the risk of bias
• The quality of reporting

Risk of Bias

Risk of Bias is a metric used when conducting systematic reviews. Chapter 7 of the Cochrane Handbook defines bias as "a systematic error, or deviation from the truth, in results". There are several tools that assist with this process.

Synthesis of Evidence

The synthesis of evidence includes a qualitative synthesis of included studies which describes study methodology, strengths and limitations, patterns across studies, potential bias in study design, and the relevance of studies to the populations, comparisons, cointerventions, settings, and outcomes or measures of interest.

The synthesis of evidence may also include a meta-analysis that pools data from included studies.  A meta-analysis will address the heterogeneity among study effects, statistical uncertainty, and the sensitivity of conclusions to changes in the protocol, assumptions, and study selection.

Reporting

When preparing your report or article, refer to the PRISMA checklist. PRISMA is an evidence based minimum set of items for reporting systematic reviews, meta-analysis, and scoping reviews. PRISMA focuses on the reporting of reviews evaluating RCT's but can also be used as a basis for reporting systematic reviews of other types of research.