Can apply to: Software packages and papers describing software packages
Metric definition: The number of times a piece of software or code (or a paper that describes software or code) has been cited as a resource in a journal article or book.
Metric calculation: Like data, software can be cited formally (in the references section of a paper) or informally (linked to from the methods section of a paper). Google Scholar searches the scholarly web for all mentions of a software package by name; Depsy searches PubMed Central Europe and ADS for mentions of a software package by name.
Data sources: Google Scholar, Depsy
Appropriate use cases: Citations to software can be interpreted to understand the influence of a software package, and in many cases the reuse of that software package in other researchers’ analyses.
Limitations: Software packages are much less likely to be cited directly than articles about software packages are. Only around a third of citations to software are formal, so attempts to count software citations using existing tools may miss important mentions of software in research articles.
Inappropriate use cases: Citations to software should not be interpreted to measure quality.
Transparency: While all sources link to the papers that cite software, the availability of these papers to the end user varies due to journal article paywalls. Though Google Scholar might link to a paper that cites a piece of software, the end user may not be able to read that paper to see the context of that citation, if they do not have a subscription to the journal in which the citing paper was published.
Timeframe: In theory, software of any age can be cited in the research literature.