APA Dictionary of Psychology

n. the format of a research study, describing how it will be conducted and the data collected. For example, an experimental design involves an independent variable and at least two groups, a treatment or experimental group and a control group, to which participants are randomly assigned and then assessed on the dependent variable. A variety of other design types exist, including correlational research, quasi-experimental designs, longitudinal designs, natural experiments, and observational studies, among others.