When referring to variables, "qualitative" is another term for categorical or nominal. When speaking of kinds of research, "qualitative" refers to studies of subjects that are hard to quantify, such as art history. Qualitative research tends to be a residual category for almost any kind of nonquantitative research.

A type of research design for conducting studies in field or real-life situations where the researcher may be able to manipulate some independent variables but cannot randomly assign subjects to control and experimental groups.