Introduction How to test a sufficient or a necessary condition with a case study

also be expressed as the sufficient condition: condition “If there is non- A, then there will be non-B”.

5.1.2 Candidate cases

A candidate case is a member of a set of cases from which the researcher will select one case or a small number of cases for a case study. For a single case study only one single instance of the object of study must be selected from the domain to which the theory is assumed to apply. This selection is essentially an arbitrary choice, which is only marginally regulated by theo- retical considerations. In this respect, the selection of a case for a single case study is similar to the choice of a population for a theory-testing survey. For a specific study, candidate cases could be selected from the entire domain, from a defined subset of the domain, or even from outside the domain e.g. to find the boundaries of the domain to which the theory applies. The exploration of “practice” at the very beginning of the research project may have provided information about where specific cases could be found. Experts and practitioners could be asked to help to make a list of candidate cases. Usually such a list is bound by regional or national boundaries and the information collected will apply to, for instance, Dutch or European instances of the object of study, whereas the domain that is specified is not defined by such geographical or political boundaries. Confining the identification of potential cases to a limited geographical domain or to another domain that is “conveni- ent”, which could be a worldwide virtual domain as well does not mat- ter much if the findings will be replicated in later studies.

5.1.3 Case selection

Case selection is the selection of a case from the candidate cases. As discussed in Chapter 4 “Theory-testing research”, the case for the sin- gle case study must be selected on the basis of the presence or absence of the dependent concept or independent concept. For testing whether A is a sufficient condition for B, there are two pos- sibilities for selecting the case: ■ selection on the basis of the presence of the independent concept “If there is A, then it is tested if there is also B”; ■ selection on the basis of the absence of the dependent concept “If there is no B, then it is tested if there is also no A” non-A is a necessary condition for non-B. For testing whether A is a necessary condition for B, there are also two possibilities for selecting the case: ■ selection on the basis of the presence of the dependent concept “If there is B, then it is tested if there is also A”; ■ selection on the basis of the absence of the independent concept “If there is no A, then it is tested if there is also no B” non-A is a sufficient condition for non-B. Depending on the objective of the research a “most likely” or a “least likely” case can be selected. A “most likely” case is an instance of the object of study in which confirmation of the hypothesis is likely. Such selection strategy can be used when the proposition is tested for the first time “initial theory-testing research”. This strategy is also pos- sible when the outcomes of earlier tests result in doubts about the sup- port for the proposition in the domain where it was tested. The researcher may then want to select a “most likely case” to find parts in the domain where the proposition could be supported. A “least likely” case is an instance of the object of study in which support for the proposition is not likely. This strategy may be used when the outcomes of earlier tests indicate support for the proposition, and the researcher wants to know what the boundaries of the domain are. This is import- ant for determining the generalizability of the theory. For case selection, as it is described here, it is necessary to measure the value of the independent or dependent concept before the actual test is conducted, i.e. before “measurement” has occurred. However, it might not be feasible to measure the value of the relevant concept at this stage of the research. In this case, an alternative strategy for case selection is that a candidate case is selected and that it is verified in the measurement phase of the research whether the concept is indeed present. If not, then the case cannot be used for testing the hypothesis and another case must be selected.

5.1.4 Hypothesis

A proposition is a statement about a relation between concepts. For testing, a proposition must be reformulated into a hypothesis. A hypothesis is a statement about a relation between variables in which the variable is a measurable indicator of the concept. In this type of theory-testing the hypothesis can be formulated quite easily. If the proposition specifies a sufficient condition and a case is selected in which the condition is present, the hypothesis is that the