An update on something that I said in this thread. I incorrectly said that our REST API performs an OR search when given multiple terms in a query or query.bibliographic query. I was wrong about that.
We don’t quite have an OR query at play within our REST API. Instead, query and query.bibliographic require that at least 20% of query words match. We added this requirement a few years ago for performance reasons. So, with 10 input query words, 20% becomes 2 words, and the query results start to drop works that match only one word at that threshold. This is why a query containing poverty+low+middle+income+country+LIC+MIC has more results than a query containing poverty+low+middle+income+country+LIC+MIC+climate+urban+migration+gender . We’ve simply dropped results from the latter of the two queries because of that 20% matching rule that we implemented.
For more context on this see this thread.
-Isaac