The type of question you are trying to answer often determines the best research design to seek. For instance, a randomized controlled trial would not be feasible for a prognosis study, so the highest level of evidence for prognosis is a cohort study.

The four most common types of questions in EBP are therapy, diagnosis, etiology, and prognosis. As the Searching the Literature module will discuss, some databases provide filters to help searchers find the appropriate study types. These filters add search terms to retrieve the study types listed below.

Though this module primarily focuses on quantitative research designs, qualitative research does play an important role in Evidence-Based Practice. How qualitative researched is described varies in different fields, but an overarching theme is that quaalitative research is research focusing on how individuals or groups view and understand their world and experiences. Authors Greenhalgh and Taylor identify two points of qualitative research in health sciences as "methods aimed to make sense of, or interpret, phenomena in terms of the meanings people bring them" and "research that defines preliminary questions which can then be addressed in quanitative studies." [4]