MGH Guides: Scoping + Systematic Reviews: What Types of Sources Will You Include and Where Will you Find Them?

Types of Sources You May Include

Systematic reviews tend to focus on evidence from studies, because their purpose is to synthesize the data from the evidence to come to a conclusion.

Scoping reviews, by contrast, often focus on evidence from studies, but can also go far beyond studies, because their purpose is to describe and characterize the available evidence.

Let's go into a little more detail about the types of sources you'll want to consider for each type of review.

(Peinemann et al., 2013)

Where to Search for Published Literature

According to Bramer et al. (2017), the ideal database combination for health sciences reviews is Medline, Embase, Web of Science Core Collection, and Google Scholar with CINAHL and/or PsycInfo if reviews in those topic areas.

Medline (through PubMed) and Google Scholar are freely available, but not everyone has access to the other databases on that list.

Discipline-Based Databases

The following is a list of the most popular discipline-specific databases available through Bellack Library

PubMed
The place every health professional and medical researcher goes to find literature. It includes Medline as well as more life sciences journal and book citations. This version will also link directly to Treadwell Library's eJournal subscriptions.

Ovid Medline
Medline represents the creme de la creme of health sciences literature, and although it is part of PubMed, some people prefer to search it separately.

CINAHL
The Cumulative Index to Nursing and Allied Health Literature can be a great supplement to PubMed for health professions literature. It contains a combination of both scholarly research articles as well as articles from trade publications.

PsycINFO
Created by the American Psychological Association, it is the premier database for psychological, behavioral, and developmental topics.

ERIC
The Education Resources Information Center is the premier database for educational literature. Good for information about school based interventions but also useful for information about school aged children, in general.

Introduction to Grey Literature

Grey literature is all of that information that is not published in books or journals. Before the web, it was much harder to locate, but any Google search will have you swimming in it in no time.

This guide will walk you through the various types and the reasons you may want to seek them out, as well as provide links to help you find what you need.

Check out this quick video from The Learning Portal to learn more about Grey Literature

Why include Grey Literature?

Conference presentations, white papers, and theses can provide an important perspective that may be missing from formally published literature. Because of a publication bias toward positive results (Joober et al., 2012), journals and books are not as likely to include studies that have null results. Grey literature sources may also contain the newest thinking and alternative viewpoints in a discipline. Not only can the formal publishing process be slow, but it can also be somewhat conservative.

In their letter to the editor, Pedersen (2024) argues that, by not including grey literature in your scoping review,

Your search is not as comprehensive as it could be, especially following JBI's guidelines,
You are not helping to reduce publication bias and skewed results, and
If you're looking to include qualitative studies, you may be missing them by not including grey literature sources,

Pedersen wraps up their letter by pointing out how important it is to include a librarian in your search creation to ensure that broader perspectives can be incorporated into your review.

Should I Include Grey Literature?

The answer to that question depends on the goals of your review. Also, if you decide to include grey literature, that doesn't mean you need to include all types of grey literature (many reviews will include data from ClinicalTrials.gov, for example, but no other grey literature sources). Here are some things to consider as you are making that decision.

Is the published, peer reviewed literature enough to capture what is known about your topic?
Is your topic fast moving, with new evidence coming out all the time? If so, grey literature could help you include the most up to date evidence, before it goes through the, often slow, process of peer review and publication.
Will grey literature offer a different perspective than is typically found in the published literature? For example, government documents can offer different types of information than you might find in a journal.

One last thing to think about: the decision to include grey literature does not have to be binary. You may opt to do something like accept only peer reviewed literature in your included studies but then cite grey literature in your background and/or discussion section to help fill out the picture.

Searching for Grey Literature

Doing a systematic search for grey literature can be a challenge. So you will want to plan carefully and document the decision making as well as the methods you use. There's more about this on the How Do You Build Your Search? page.