Empirical Research: A type of research that is based on information collected through observation or experiment rather than theory. Empirical studies aim to objectively test and investigate specific questions or hypotheses through verifiable methods. . . . Empirical research can be quantitative or qualitative in nature.
The sage glossary of the social and behavioral sciences. Edited by Larry E. Sullivan. Sage Publications, 2009.
Methodologies such as literature reviews, systematic reviews and retrospective studies are not types of empirical research.