I’ve talked [quite a bit] about the importance of identifying the works underlying a given book entry in a catalogue (which would be an item or manifestation in FRBR lingo). Our effort was based on trying to find cases of two manifestations/item which we thought shared a common work. The results were as follows:
This compares reasonably well with OCLC’s prior work in this regard (Hickey, Thomas. FRBR algorithms & tools online. Dublin, Ohio: (OCLC), June 20, 2002) which found that in WorldCat around 80% of records reflected a single manifestation per work.