For those of you who don’t know OAIster, if you have any reason to search for digitized primary sources, you should check it out. It’s a union catalog of digital library holdings. It’s chief asset is wonderfully descriptive metadata. And like with other collections of collections, I recommend searching OAIster to find which digital collections contain the kinds of things you’re interested in, and then searching or browsing those collections individually.
For those of you who know OAIster, you know that it recently stopped being its own unique entity and started being an OCLC-hosted entity. It’s now available on the FirstSearch interface and the WorldCat.org interface. (Here’s more on the history of the catalog.)
Enter the oddness. My co-worker ran some identical searches on both interfaces and came up with startlingly different numbers of results for most of her searches. Confused, I contacted OAIster and have just heard back from them why this is so. Apparently, the “keyword” search in the FirstSearch interface searches through the Source, Subject, Title, and Notes indexes. The keyword search on the WorldCat.org interface searches all available fields and all indexes.
So now we know.