Case study
The case study is one of several ways of doing social science research. Other ways include experiments, surveys, multiple histories, and analysis of archival information (Yin 2003).
Rather than using large samples and following a rigid protocol to examine a limited number of variables, case study methods involve an in-depth, longitudinal examination of a single instance or event: case. They provide a systematic way of looking at events, collecting data, analyzing information, and reporting the results. As a result the researcher may gain a sharpened understanding of why the instance happened as it did, and what might become important to look at more extensively in future research. Case studies lend themselves to both generating and testing hypotheses (Flyvbjerg, 2006).
Yin (2002), on the other hand, suggests that case study should be defined as a research strategy, an empirical inquiry that investigates a phenomenon within its real-life context. Case study research means single and multiple case studies, can include quantitative evidence, relies on multiple sources of evidence and benefits from the prior development of theoretical propositions. He notes that case studies should not be confused with qualitative research and points out that they can be based on any mix of quantitative and qualitative evidence.  Single-subject research provides the statistical framework for making inferences from quantitative case-study data. This is also supported and well-formulated in (Lamnek, 2005): "The case study is a research approach, situated between concrete data taking techniques and methodologic paradigms."

# Case selection
When selecting a case for a case study, researchers often use information-oriented sampling, as opposed to random sampling (Flyvbjerg, 2006). This is because the typical or average case is often not the richest in information. Extreme or atypical cases reveal more information because they activate more basic mechanisms and more actors in the situation studied. In addition, from both an understanding-oriented and an action-oriented perspective, it is often more important to clarify the deeper causes behind a given problem and its consequences than to describe the symptoms of the problem and how frequently they occur. Random samples emphasizing representativeness will seldom be able to produce this kind of insight; it is more appropriate to select some few cases chosen for their validity.
Three types of information-oriented cases may be distinguished:
- Extreme or deviant cases
- Critical cases
- Paradigmatic cases.

## Extreme case
The extreme case can be well-suited for getting a point across in an especially dramatic way, which often occurs for well-known case studies such as Freuds Wolf-Man.

## Critical case
A critical case can be defined as having strategic importance in relation to the general problem. For example, an occupational medicine clinic wanted to investigate whether people working with organic solvents suffered brain damage. Instead of choosing a representative sample among all those enterprises in the clinics area that used organic solvents, the clinic strategically located a single workplace where all safety regulations on cleanliness, air quality, and the like, had been fulfilled. This model enterprise became a critical case: if brain damage related to organic solvents could be found at this particular facility, then it was likely that the same problem would exist at other enterprises which were less careful with safety regulations for organic solvents. Via this type of strategic sampling, one can save both time and money in researching a given problem. Another example of critical case sampling is the strategic selection of lead and feather for the test of whether different objects fall with equal velocity. The selection of materials provided the possibility to formulate a generalization characteristic of critical cases, a generalization of the sort, If it is valid for this case, it is valid for all (or many) cases. In its negative form, the generalization would be, If it is not valid for this case, then it is not valid for any (or only few) cases.

## Paradigmatic case
A Paradigmatic case may be defined as an exemplar or prototype. Thomas Kuhn has shown that the basic skills, or background practices, of natural scientists are organized in terms of exemplars or 'paradigms' the role of which in the scientific process can be analyzed. Similarly, scholars like Clifford Geertz and Michel Foucault have often organized their research around specific cultural paradigms: a paradigm for Geertz lay for instance in the deep play of the Balinese cockfight, while for Foucault, European prisons and the Panopticon are examples. Both instances are examples of paradigmatic cases, that is, cases that highlight more general characteristics of the societies or issues in question. Kuhn has shown that scientific paradigms cannot be expressed as rules or theories. There exists no predictive theory for how predictive theory comes about. A scientific activity is acknowledged or rejected as good science by how close it is to one or more exemplars; that is, practical prototypes of good scientific work. A paradigmatic case of how scientists do science is precisely such a prototype. It operates as a reference point and may function as a focus for the founding of schools of thought.
For more on case selection, see 

# Generalizing from case studies
The case study is effective for generalizing using the type of test that Karl Popper called falsification, which forms part of critical reflexivity (Flyvbjerg, 2006). Falsification is one of the most rigorous tests to which a scientific proposition can be subjected: if just one observation does not fit with the proposition it is considered not valid generally and must therefore be either revised or rejected. Popper himself used the now famous example of, "All swans are white," and proposed that just one observation of a single black swan would falsify this proposition and in this way have general significance and stimulate further investigations and theory-building. The case study is well suited for identifying "black swans" because of its in-depth approach: what appears to be "white" often turns out on closer examination to be "black."
For instance, Galileos rejection of Aristotles law of gravity was based on a case study selected by information-oriented sampling and not random sampling. The rejection consisted primarily of a conceptual experiment and later on of a practical one. These experiments, with the benefit of hindsight, are self-evident. Nevertheless, Aristotles incorrect view of gravity dominated scientific inquiry for nearly two thousand years before it was falsified. In his experimental thinking, Galileo reasoned as follows: if two objects with the same weight are released from the same height at the same time, they will hit the ground simultaneously, having fallen at the same speed. If the two objects are then stuck together into one, this object will have double the weight and will according to the Aristotelian view therefore fall faster than the two individual objects. This conclusion seemed contradictory to Galileo. The only way to avoid the contradiction was to eliminate weight as a determinant factor for acceleration in free fall. Galileos experimentalism did not involve a large random sample of trials of objects falling from a wide range of randomly selected heights under varying wind conditions, and so on. Rather, it was a matter of a single experiment, that is, a case study.
Galileos view continued to be subjected to doubt, however, and the Aristotelian view was not finally rejected until half a century later, with the invention of the air pump. The air pump made it possible to conduct the ultimate experiment, known by every pupil, whereby a coin or a piece of lead inside a vacuum tube falls with the same speed as a feather. After this experiment, Aristotles view could be maintained no longer. What is especially worth noting, however, is that the matter was settled by an individual case due to the clever choice of the extremes of metal and feather. One might call it a critical case, for if Galileos thesis held for these materials, it could be expected to be valid for all or a large range of materials. Random and large samples were at no time part of the picture.
By selecting cases strategically in this manner one may arrive at case studies that allow generalization.
For more on generalizing from case studies, see 

# History of the case study
As a distinct approach to research, use of the case study originated only in the early 20th century. The Oxford English Dictionary traces the phrase case study or case-study back as far as 1934, after the establishment of the concept of a case history in medicine.
The use of case studies for the creation of new theory in social sciences has been further developed by the sociologists Barney Glaser and Anselm Strauss who presented their research method, Grounded theory, in 1967.
The popularity of case studies in testing hypotheses has developed only in recent decades. One of the areas in which case studies have been gaining popularity is education and in particular educational evaluation. Some of the prominent scholars in educational case study are Robert Stake and Jan Nespor (see references).
Case studies have also been used as a teaching method and as part of professional development, especially in business and legal education. The problem-based learning (PBL) movement is such an example. When used in (non-business) education and professional development, case studies are often referred to as critical incidents (see David Tripp in references).

## History of Business Cases
When the Harvard Business School was started, the faculty quickly realized that there were no textbooks suitable to a graduate program in business.  Their first solution to this problem was to interview leading practitioners of business and to write detailed accounts of what these managers were doing.  Of course the professors could not present these cases as practices to be emulated because there were no criteria available for determining what would succeed and what would not succeed.  So the professors instructed their students to read the cases and to come to class prepared to discuss the cases and to offer recommendations for appropriate courses of action.  Basically that is the model still being used.  See a critique of this approach.