Systematic Reviews: What is a systematic review?

In the health-related professions, systematic reviews are considered the most reliable resources.  They are studies that make up the top level of the evidence-based information pyramid, and as a result, they are the most sought after information for questions about health. Systematic reviews are not quite the same as literature reviews. Literature reviews, also known as narrative reviews, attempt to find all published materials on a subject, whereas systematic reviews try to find everything that focuses on answering a specific question.  Since systematic reviews are generally associated with health related fields, their main objective is to ensure the results of the review provide accurate evidence that answers relevant questions.  If you are looking for information about literature reviews, please check the library's guide on the topic here.

When looking for answers to health questions, systematic reviews are considered the best resources to use for evidence-based information.  The predefined protocols, the amount of information reviewed, the evaluation process involved, and the efforts to eliminate bias are all a part of what makes health professionals consider systematic reviews to be the highest level of evidence based information available.  As a part of the process, systematic reviews tend to look at and evaluate all the randomized controlled trials, or all the cohort studies, for their specific topic.  By looking at and evaluating a vast amount of comparable studies, a systematic review is able to provide answers that have a much stronger level of evidence than any individual study.

These reviews collect large amounts of information that fit within the predetermined parameters, so performing a systematic review is an excellent way to develop expertise on a topic.  Setting up the criteria, searching for the information, and evaluating the information found, gives the reviewer an extremely strong understanding of the process needed to create a review as well as how to evaluate its various elements.  Creating a systematic review gives the reviewer an opportunity to further the discussion on a topic.  In the health fields, performing and then publishing these reviews provides more evidence on topics that can be used for making decisions in a clinical environment.

There are a number of databases that focus on health related resources, and most of them search through journals that include systematic reviews.  In these cases, you can include the words “systematic review” and the results will include entries that have the words “systematic review” in them somewhere.  Many of these results will be systematic reviews; however, some of the results may include these words, but are not systematic reviews.  A few databases that are used by researchers have added in limitation features that make it easier to find systematic reviews, and ensure a specific article/document/publication type are found.  Here are three examples of databases and how to limit their search results to systematic reviews:

• PubMed  
  • Scroll down the main page and in the middle column, click on Clinical Queries.  In the provided search box type in your search terms.  The middle row of results is systematic reviews.  You can type your search terms in on the main page, and limit the results after they are listed.  To do this, find the section for “article types” on the left side of the page and click “customize”.  On the list that pops up, clear all the check boxes except the one for “systematic reviews”, then click “Show”.  When the main page is displayed again, click on “systematic reviews” to reset the search using that limit.
• CINAHL
  • In CINAHL (EBSCO version) it is easy to limit search results to systematic reviews from the initial search page.  Scroll down to find “Publication types” on the right side of the page.  In the Publication Types box, search through the list until you find systematic reviews and highlight it.  After this has been done, add in any other limits needed and then search as usual.
• TRIP database
  • This is the easiest of the three to use for finding systematic reviews.  On the main search page, type in the terms, run the search and wait for the results page.  On the results page, the right side has a limit that says “systematic review”.  Click on it and the results will all be systematic reviews.

These are a few of the various types of systematic reviews.

Critical review

Critical reviews are often thought to be the same as a literature review.  They involve a comprehensive review of a topic that involves a high level of analysis that seeks to identify the most important aspects of a subject.

Overview

The overview is a look at the literature available on the topic.  They may or may not have an analytical component that provides a synthesis of the information found, but this depends on how systematic the review has been.

Qualitative systematic review

This type of study looks at as many qualitative studies and tries to find themes among these studies that lie across the range of reviews. The information is then organized into a narrative that is frequently accompanied by a conceptual model.

Rapid review

The number of studies included in a rapid review are dictated by time constraints. Most often these reviews are conducted to determine what is known about policies or practices, and then determine how much these are based on evidence.

Scoping review

These reviews are intended to quickly assess the availability of research on a specific topic, and then determine whether the evidence provided in these research articles is sufficient and appropriate, 

Umbrella review

Umbrella reviews research broad topic, and look at a wide range of reviews that have been done for a number of potential interventions. It then triest to establish the pros and cons of each treatment and what the potential results would be.