Topic: Systematic Searching for Evidence Synthesis

To reduce confusion, the information below uses the following terminology:

Original source: the source whose references and citations interest you

References: items cited by the original source

Citations: later sources that cite your original source

Sources that meet your inclusion criteria are an excellent resource for finding more relevant sources. To find sources directly related to your original source, you can do two forms of citation chasing:

1. Backward (or ancestral) citation chasing: looking at the references cited by your original source
2. Forward citation chasing (or cited reference searching): looking for citations of your original source

For backward citation chasing, it's easy to be sure you have all the references, since you have the original source itself right in front of you. In addition, some research databases let you view these lists in a way that lets you search or export the references.

Forward citation chasing, or cited reference searching, is more challenging. There's no way to search comprehensively in a forward direction using a single database or other tool. What you're seeing is limited to the segment of the published or unpublished literature that database is aware of, which means it's only a subset of all possible citing references. To be as complete as possible in locating citations, you can try a combination of databases and may want to add Google Scholar to the process.

There are also automated tools that can make both backward and forward citation chasing quicker and more efficient. Because these are so convenient, we'll start there.

There are two excellent tools for automating the citation chasing process. They both use the Lens.org API to access the Lens dataset which, while not comprehensive, is expansive. The Lens includes data from CrossRef, ORCID, PubMed, CORE, the US and European patent offices, among other sources.

Since they use the same data source, the main differences between citationchaser and SpiderCite are interface and input options. Both have detailed instructions.

If this is part of your systematic searching process, remember to track the numbers of references and citations for your PRISMA flow diagram or whatever reporting tool you're using. Be sure to document and cite your use of automated tools in your methods as well.

citationchaser allows you to input your original source or sources in multiple ways. If you have only a single or small set of sources you want to search, it's probably easiest to paste in the Digital Object Identifiers (DOIs), PubMed identifiers (PMIDs), or some other unique identifier that citationchaser recognizes. For a larger set of original sources, export the batch from your citation management tool as an RIS file and upload that to citationchaser instead. Once the search is complete, you'll be able to export both references and citations to your citation manager.

SpiderCite doesn't allow for identifier searching. You'll need to export the original sources from your citation manager in RIS, XML, or BibTex format and then upload that file. As with citationchaser, you'll be able to export the references and citations SpiderCite locates.

For forward citation chasing, Scopus displays a grey box one the right listing the number of citations found in Scopus. Tap the View all citing documents link at the bottom of the box to see all of them as a list of search results you can view and export.

For backward citation chasing, scroll below the article information to References. Tap the link on the right to view those references in search results format for viewing and exporting.

Scopus also lets you see "related documents." In Scopus, these are sources that have references in common with your original source. Scroll down below the article information to find the Related documents box on the right, then tap View all related documents based on references link at the bottom of the box to see all of them as a list of search results you can view and export.

The list on the related documents page is automatically sorted by relevance. In this case, relevance is based on the number of references in common with your original source, but Scopus does not tell you how many shared references there are in each related document.

Google Scholar allows forward citation chasing only. For the article below, Google Scholar shows 71 citations. The number is usually higher than what you'd see in a research database, and may include errors (source is not cited) or questionable publications. However, since Google Scholar's search is so large and interdisciplinary, it may include some legitimate citations you won't see elsewhere. 

To search within the articles Google Scholar believes have cited your original source, tap Cited by (number), check the box for Search within citing articles, and add terms in the search box at the top of the page.

Some databases offer the ability to view references, citations, or both. As a reminder, what you're seeing in the forward direction is limited to what that database is aware of (e.g., what journals it indexes, or what data is provided by the publisher), which means it's only a subset of all possible citations.

This article in APA PsycInfo includes both the references (1) and citations (2):

The images below are from PubMed. "References" are references from the original source, and "Cited by" are citations to that source.