Why does the web site not allow one to use a Boolean OR in searching?

Basically, the Boolean OR is incompatible with faceted searching. Here's an example od the core problem:

Say a user searches on "cat OR dog" because his/her research is on whether cat owners are happier than dog owners. On the search results page s/he then clicks on "United States" to narrow the search to U.S. data.

What the user doesn't realize is that by clicking on "United States" s/he has excluded all search results relating to cats because ICPSR has no U.S. data on cats.

This is the real problem. By using a facet, the user has dropped a query term but has no indication of this before or after the click. The same thing can happen with faceting by data format, subject term, etc.

For this reason, ICPSR is not adding a Boolean OR to our study search.

In further support of our website users, please also note that faceted searching is used for all searches conducted on the website (studies, variables, citations). One of the guiding principles in website design is to make sure that all interfaces, in this case searches, follow the same rules. We don't want users to have to learn different syntax rules on different pages, especially when the searches look identical.