Method of Agreement

Conceptual Overview and Discussion

The method of agreement was developed by John Stuart Mill. Mill argues that systematic comparison of social phenomena contributes to the development of empirical generalizations. Next to the method of agreement, he describes the method of difference as an obvious method of comparison. Here, instances of a social phenomenon are compared with instances where this phenomenon does not occur, but that are similar in most other respects. He developed his logic of inquiry with the purpose of applying it in experimental inquiry, but his logic also became applied to comparative case study research. Here it was directed at comparing cases of the same social phenomenon that appears in very different circumstances. This is also called a most different research design, since most (independent) variables differ between these cases.

However, the use of the method of agreement in a multiple-case design is controversial. John Stuart Mill already refers to the fact that the method of agreement is incapable of identifying a plurality of causes; phenomena that follow from different instances or combinations of instances. Charles Ragin further works out this critique by arguing that most social phenomena have multiple social causations. When using the method of agreement, phenomena caused by either one particular instance or by another particular instance may be falsely judged to have none of these instances as a cause. For example, one social revolution may be caused by land hunger and another by rapid commercialization. By comparing these cases using the method of agreement, both explanatory causes would be falsely rejected on the basis of their absence in the other case. Alexander George and Andrew Bennett later called this issue the problem of equifinality.

The method of agreement therefore runs the risk of falsely eliminating causes of social phenomena. Because of this defect, Ragin pleads for a double application of the method of agreement, namely the indirect method of difference. This means the controlled comparison takes two successive steps. Researchers should look for instances of a social phenomenon that have only very few circumstances in common (the method of agreement). After identifying possible causal conditions in this way, researchers should also look for instances where the social phenomenon is absent. Only if the conditions that are supposed to cause the phenomenon are absent in all cases where the phenomenon is absent, can a causal relation can be identified.

A second reason that the method of agreement is controversial is the fact that most social phenomena follow from a combination of causes. Ragin calls this conjunctural social causation. When a phenomenon is caused by a combination of instances, single instances may be falsely judged as having no explanatory force, while in combination they may explain the occurrence of the phenomenon. For example, the work motivation of people may be caused by a combination of nice colleagues and profitable reward. With the method of agreement, profitable reward would be falsely rejected as an explanatory cause when the researcher examines cases where this reward is present but nice colleagues are absent. This problem is also not solved by a double application of the method of agreement. Work motivation would be absent in cases where either nice colleagues or profitable reward is absent.

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