A case study is a method for learning about a complex instance, based on a comprehensive understanding of that instance obtained by extensive description and analysis of that instance taken as a whole and in its context."

For example, if we were asked to study what caused the Three Mile Island disaster and scoped the job to describe whether required safeguards were complied with, this would not be a case study. If, however, we scoped the job to examine in depth events leading up to the disaster, what went wrong, and why it went wrong, this would be a case study.

For a second example, if we were asked to study the safety of nuclear plants in general, we might select as our method a survey of self-reported compliance with safeguards in all existing plants. This would not be a case study. If, however, we scoped the job to examine in depth recent problems in appropriately selected nuclear plants including among others Three Mile Island, seeking to understand why the safeguards either were not complied with or were not sufficient, then we would have selected the case study method to answer the question.

Common Benefits Expected From Case Study Evaluations

• Longitudinal - Assurance that a short-term situation that may be unrepresentative of what is happening isn’t inflated in importance.

• Triangulation - Assurance that reasons given for events properly reflect influences from many different sources.

• Purposive instance - Ability to match questions asked and later generalization of findings at level appropriate to the questions.

Analysis

Assurance of the ability to collect data needed to test alternative interpretations and to make rapid adjustments in design.

Search for disproving-proving evidence - Assurance that alternative interpretations

have been thoroughly searched for and checked; thorough identification of instances that don’t fit the general pattern; and, often, understanding of the reasons for the outliers.

Reporting

Assurance of authenticity through and ease of recall; use of the tendency to generalize from personal experience but via the substitution of more objective experience for anecdotes of unknown credibility.