Inclusion and exclusion criteria in research are the characteristics the subject must have, or cannot have, in order to be counted in the research data. The formulation of clear inclusion and exclusion criteria is one of the researcher's first tasks and will play an important part in the research proposal.

In research related to nursing, the most obvious inclusion and exclusion criteria relate to the physical characteristics of the patient. The study may, for instance, relate to the incidence of breast cancer in women between the ages of forty and sixty. Clearly, a woman of thirty or a man of any age is excluded from this study, while a woman of forty-five would be within the inclusion criteria.

In practice, nursing research is often much narrower than that in the study outlined above, and the inclusion and exclusion criteria may be very detailed. They might include the medication the patient has been receiving or various combinations of underlying conditions from which the patient suffers.