Parts of an Evidence Synthesis
While the contents of an evidence synthesis vary based on the type of synthesis being done (see ES Types), most good evidence syntheses do share a number of core components:
Introduction
A brief background on the topic that describes its context and importance
Review Question
The specific question or evidence gap to be explored by the evidence synthesis.
Inclusion Criteria
The inclusion criteria (which can also be framed as exclusion criteria in some ESs) are the guidelines that reviewers follow when determining whether a specific item will be considered in the evidence synthesis. These criteria should be rigidly adhered to and constitute a promise to the readers by the reviewers that only the items that fit all the criteria were included in the review.
Participants
The participants section includes a description of the population(s) of interest in the review.
Phenomenon / Exposure / Intervention
The phenomenon / exposure / intervention usually describes the main issue of interest in the evidence synthesis.
Types of Studies
The types of studies section typically lists the types of research that were considered for inclusion. The specific contents of this section vary widely between the types of syntheses and even within types as it is influenced by the amount of research available and by the types of research that have been performed. Additionally, this is the one section where the criteria may be a little more flexible, as it may include a statement like "other types of studies were considered for inclusion if they were deemed to be highly relevant and of good quality."
Methods
The methods section includes a detailed description of how the evidence synthesis was carried out. Because evidence syntheses are done based on a prescribed set of rules and criteria, most methods sections contain the same types of information.
Search strategy
The search strategy section describes how the search how search terms were generated and how the search protocol was developed, what databases were used, the date that the search was performed, and whether any grey literature sources were searched.
Note that while the search strategy / protocol is often very complex and reflects a similar approach when it is being used in traditional article databases, grey literature searching in systematic reviews does not follow the same criteria. Few grey literature sources are large or sophisticated enough to make the use of advanced searching strategies practical, but are often included in the search strategy as a way to mitigate the effects of publication bias.
Study selection
The study selection section describes the process by which the two (or more) reviewers selected items for inclusion in the review. It includes such information as the number of reviewers, the appraisal ratings that were considered acceptable and how they were obtained, and how differences of assessment were resolved between reviewers.
Data extraction
The data extraction section (which can go by other names) describes how information from each included article / item was recorded and used. In the case of quantitative ESs, for example, specific information is usually extracted and recorded in table to make comparisons between studies (then arranged in rows) easier.
Results
The results section describes the outcomes of each of the processes implemented in the methods. It provides information about the number of studies included, the appraisals of the studies, and a brief description of the studies.
Study inclusion (and PRISMA diagram)
The study inclusion section details the number of studies that were retrieved, the number of duplicates removed, the number that were considered relevant, the number that passed the appraisal criteria and the total number of studies that were finally considered for review. This information is almost always provided in the form of a short paragraph, and is sometimes also provided in the form of a PRISMA Flow Diagram. There may also be a summary of the most common reasons that articles were excluded from the review.
Methodological quality
The methodological quality section provides a summary of the overall appraised quality of the included articles. This typically includes a brief paragraph and a more detailed table that summarizes the appraisals for each article.
Characteristics of included studies
This section provides a quick overview of the specific details of the studies that were included, such as study type, number of participants, and geographical location. It does not typically include mention of the outcomes of the studies.
Review Findings
This section describes the overall findings of the evidence synthesis.
Discussion
This section discusses the review findings in the context of the literature and in practice.
Appendix - Search strategy or strategies
This section contains a copy of the exact search that was performed in at least one of the databases (some reviews include copies of all the searches performed). It does not include results of those searches, but instead provides insight into the keywords, subject terms, proximity searches, Boolean operators, etc. that were used to retrieve the items for review.
