A frequently asked question is, "When should one choose to conduct a case study, rather than an experiment?" To answer this question, it is important to understand some basic differences between case-study methods and experimental designs. Experiments allow the researcher to manipulate the independent variables (those under the control of the experimenter) that are being studied.
For example, in a study to determine the most effective treatment approach for severe depression, subjects could be randomly assigned to one of three different treatments. The treatments are under the control of the researcher in the sense that he or she determines who will get a particular treatment and exactly what it will be. On the other hand, case studies are used in situations where the variables cannot be manipulated. Experiments typically, although not exclusively, are performed in a laboratory setting. Case studies occur in naturalistic settings, a research environment in which, in contrast to laboratory research, subjects are studied in the environment in which they live, with little or no intervention on the part of the researcher. Experiments are characterized as having rigorous control over extraneous variables. Case studies typically lack such control. Experiments place a heavy emphasis on data-analysis procedures that use numbers and statistical testing. Case studies emphasize direct observation and systematic interviewing techniques, and they are communicated in a narrative form. Experiments are designed so that they can be repeated. Case studies, by their very nature, can be quite difficult to repeat.
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