In my experience using several search options or filters, it seems to be best to use radio buttons or check boxes to refine the search criteria.

I was able to find an interesting study on Visual Searching vs. Text Searching which you might find useful: http://www.ala.org/ala/mgrps/divs/lita/ital/252006/number3september/fagan.pdf

Hope this helps!

In my experience using several search options or filters, it seems to be best to use radio buttons or check boxes to refine the search criteria.

I was able to find an interesting study on Visual Searching vs. Text Searching which you might find useful.