Although there is no one database that represents every publication in the world, there are nonetheless many that contain large quantities of titles. Amazon, Alibris and the web sites of other booksellers are such databases, and access to them is free. Library holdings can be compared against these lists. It is, however, more efficient to use the WorldCat database and bypass the trouble of searching individual titles or interpreting the data or feeling the limitations of the universe of these databases. That said the universes of booksellers are good quantitative and qualitative supplemental measurements.
It is important to know the specialization or general characteristics of the booksellers’ lists and find the one that coincides with characteristics of your research. Amazon, for example, is useful for exploring the strength of the library's collection in recent publications or ones that include popular works. To narrow the results, Amazon provides useful breakdowns of subjects, e.g., biographies of women, in the U.S., in the nineteenth century. In addition, there is a good, though limited, "Advanced Search" feature. This advanced search allows one to set limits, though Amazon's options are not as useful as those in FirstSearch. It is worthwhile, however, to check back from time to time; three years ago, the language choices were only “All” and “Spanish.”
It should be no surprise that the total results from Amazon and others are much smaller than that of WorldCat, as the latter contains larger quantities of older titles, foreign language titles, and all formats. Depending on the purpose of the analysis, this might be an advantage if you have very limited time in which to be comparing the retrieved titles to the library's catalog.
Amazon also offers a large array of prize-winner lists, many of which go back to the first award issued. Against these lists the holdings of the library can be compared and the richness of the collection analyzed. Although prize-winners are not unique titles, they nonetheless can be said to represent quality within the collection.