We have updated the audience level experimental service pages.
In this initiative we are using the pattern of holdings across different types of libraries (school, research, etc) to give a 'hint' about the level of interest of an item (juvenile, research/specialist, ...). You can read more about how we calculate the levels on the project page:
Recognizing that different types of libraries typically serve different populations, OCLC researchers considered whether library types could be related to audience levels. They decided to explore whether the pattern of holdings of materials in WorldCat might be leveraged to provide an audience-level indicator. [Audience Level [OCLC - Projects]]
We have used the audience level on internal projects where materials need to be filtered in a particular way. In Worldcat identities we show an average audience level for an author (Gordon Korman gets 0.17). In this service we roll things up to the work level, and we show a list of manifestations (editions, etc) for each work.
My colleagues constructed an experiment to compare the results we got with this approach with cataloguer assessments. The audience level 'hint' compared reasonably well with the human assignments. A paper on this work will be published in due course.
'Audience level' may not be quite the right name for this. Classics for example will get lower level than you might expect if you just think about 'difficulty'. Thus spake Zarathustra, for example, has a level of 0.38: because of its 'classic' status it is widely available through public libraries.
The experimental service pages have a nice slider feature to show different audience levels in a collection of Zoology books (which were used in the experiment). (And we link all titles through to worldcat.org.)