If you have a loose idea on a topic but do not know enough yet to narrow, here's a fast way to see what is out there and how you might want to narrow it down.
While not empirical research they can give you a faster picture of what is going on in a given area as well as link you back to more research articles that are empirical. Systematic and Metanalysis are usually of better quality.
To filter by methodology, use the filter options on the main search page rather than the results list.