Modes of Generalisation From a Single Case

The idea with an evaluation is to learn from what has been done in order to be able to do it better next time. The object of an evaluation is some kind of a complex functioning unit. Most often the evaluation is conducted in a naturalistic setting and with a multitude of methods. It is an evaluative case study. The transference of knowledge from an evaluative case study to other cases is done through some kind of generalisation. In my paper I will elaborate on the different modes of generalisation from a single case. Generalisations from cases are not statistical, they are analytical. They are based on reasoning. There are three principles of reasoning: deductive, inductive and abductive. Generalisations can be made from a case using one or a combination of these principles. When a generalisation is based on the deductive principle, the procedure is similar to an experiment: a hypothesis is formulated, and testable consequences are derived by deduction. By comparing the expected findings, which are deduced from a theory and a case, with the empirical findings, it is possible to verify or falsify the theory. As a result it is possible to define the domain within which the theory is valid more exactly. Cases that are pivotal to the theory are selected. The testing of the theory is comprised of the emulation of experimental method in a naturalistic setting. From a theory and the facts of a case, generalisations are drawn concerning the domain of the theory. This kind of generalisations from a case are favoured by Robert Yin. A second mode of generalisation is achieved through induction. In case studies this is done through inductive theory-generation, or conceptualisation, which is based on data from within a case. The result is a theory normally consisting of a set of related concepts. This is how generalisations are done according to Grounded Theory. The third type of generalisation depends on the principle of abduction. The concept of abduction was coined by the pragmatist philosopher Charles Sanders Peirce. Abduction is the process of facing an unexpected fact, applying some rule (known already or created for the occasion), and, as a result, positing a case that may be. There is also another kind of abduction, says Peirce, “where we find that in certain respects two objects have strong resemblance, and that they resemble one another strongly in other respects”. Now, returning to the topic of generalising from a case, these two kinds of abduction indicate two more possible types of generalisation. One is when a case is created (reconstructed) by a process of abductive reasoning from a few facts; for instance, historical data or clues. Carlo Ginzburg, historian, refers to this kind of generalisations as the “evidential paradigm” in social sciences. The other kind of generalisation, based on abduction, is operative when generalisations are made from known cases and applied to an actual problem situation by making appropriate comparisons. This is also called naturalistic generalisation by Robert Stake. Designers practise naturalistic generalisation when they refer to their repertoire of familiar cases in implementing new designs. I will conclude by summarizing the characteristic features of the different modes of generalisations, which can be used in evaluative case studies.