Changes to WorldCat® Holdings in PlumX Metrics

In 2013, PlumX Metrics partnered with OCLC to add WorldCat® library book holdings* as a usage metric. Holdings are an important metric to help librarians, researchers and others to understand the impact of research in disciplines where books represent a significant portion of the research output. In PlumX metrics, we track well over 4 million books.

With this release, we have made some improvements to how we incorporate WorldCat® holdings in PlumX Metrics. These changes came after much analysis of the identifiers used to identify books in WorldCat (ISBN and OCLC numbers) and lay the groundwork for refreshing our holdings metrics, which have been out-of-date since 2018 (link to audit log). Over the next few months, you will see changes in WorldCat holdings counts on book artifacts that may be different from what you see today.

We will now be taking the most recent holdings count returned by WorldCat® instead of the highest. This is so that we can more accurately represent the number of institutions* that claim a holding on a given book edition*. We have worked with WorldCat® to determine that the most recent count we receive more accurately reflects the total number of institutions that claim a holding on a given book.

As a result of this change, a book artifact’s holdings count may decrease. Over time, as we refresh our corpus of book data with WorldCat®, the numbers should increase again but they might not be as high as they have been in the past. Additionally, our counts will differ from what you see in the WorldCat® public interface. The public interface counts institutions (branches comprised) that claim holdings on a given work* while the API we use to obtain holdings counts number of institutions (branches comprised) that claim holdings on a given edition as our artifacts most closely represent the edition. This may or may not equate to copies of that edition (for example, a library that holds 5 copies of a book gets a holding count of 1).

We believe that the changes we are making present a more accurate picture of library holdings on a book.


Holding: a claim of ownership

Work: a distinct artistic or intellectual creation

Edition: a specific iteration of a work, usually denoted as a new edition by modifications to the intellectual content contained therein

Institution: a grouping of one or more library branches