Google comes up with total book estimates and then explains how they arrived at the various numbers. If nothing else, it will show the non-cataloger is not as easy as it looks and many types and sources of bibliographic info exist.

As to the accuracy of the numbers. We’ll leave that to the experts, people with the tools to not only access the data but to also manipulate it in a number of ways.

From Inside Google Book Search

One definition of a book we find helpful inside Google when handling book metadata is a “tome,” an idealized bound volume. A tome can have millions of copies (e.g. a particular edition of “Angels and Demons” by Dan Brown) or can exist in just one or two copies (such as an obscure master’s thesis languishing in a university library). This is a convenient definition to work with, but it has drawbacks. For example, we count hardcover and paperback books produced from the same text twice, but treat several pamphlets bound together by a library as a single book.

You’ll then read about ISBN’s, SBN’s, Library of Congress Accession Numbers, and OCLC Accession Numbers.

Then, Google begins their explanation of how they count.


So what does Google do? We collect metadata from many providers (more than 150 and counting) that include libraries, WorldCat, national union catalogs and commercial providers. At the moment we have close to a billion unique raw records. We then further analyze these records to reduce the level of duplication within each provider, bringing us down to close to 600 million records.

Does this mean that there are 600 million unique books in the world? Hardly. There is still a lot of duplication within a single provider (e.g. libraries holding multiple distinct copies of a book) and among providers — for example, we have 96 records from 46 providers for “Programming Perl, 3rd Edition”. Twice every week we group all those records into “tome” clusters, taking into account nearly all attributes of each record.

Next, the “trust” they assign to various data sources.

When evaluating record similarity, not all attributes are created equal. For example, when two records contain the same ISBN this is a very strong (but not absolute) signal that they describe the same book, but if they contain different ISBNs, then they definitely describe different books. We trust OCLC and LCCN number similarity slightly less, both because of the inconsistencies noted above and because these numbers do not have checksums, so catalogers have a tendency to mistype them.

“We put even less trust in the “free-form” attributes such as titles, author names and publisher names.”


We tend to rely on publisher names, as they are cataloged, even less. While publishers are very protective of their names, catalogers are much less so.


So after all is said and done, how many clusters does our algorithm come up with? The answer changes every time the computation is performed, as we accumulate more data and fine-tune the algorithm. The current number is around 210 million.

But that’s not the end. They post goes on to mention what types of material (non-books) they exclude from the Google total:

+ Microforms (8 million)
+ Audio Recordings (4.5 million)
+ Videos (2 million)
+ Maps (another 2 million)
+ T-Shirts with ISBNs (about one thousand),
+ Turkey probes (1, added to a library catalog as an April Fools joke), and other items for which we receive catalog entries.

[Our emphasis] Counting only things that are printed and bound, we arrive at about 146 million. This is our best answer today. It will change.

Finally, what to do about serials and government documents?

Our handling of serials is still imperfect. Serials cataloging practices vary widely across institutions. The volume descriptions are free-form and are often entered as an afterthought. For example, “volume 325, number 6”, “no. 325 sec. 6”, and “V325NO6” all describe the same bound volume. The same can be said for the vast holdings of the government documents in US libraries [What about government docs from other countries, the UN, and ngo’s?] At the moment we estimate that we know of 16 million bound serial and government document volumes. This number is likely to rise as our disambiguating algorithms become smarter.

After we exclude serials, we can finally count all the books in the world. There are 129,864,880 of them. At least until Sunday.

Source: Inside Google Book Search

Via Resource Shelf


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