Comparative politics is a subfield of political science, characterized by an empirical approach based on the comparative method. Arend Lijphart argues that comparative politics does not have a substantive focus in itself, but rather a methodological one: it focuses on “the how but does not specify what of the analysis”.
In other words, comparative politics is not defined by the object of its study, but rather by the method it applies to study political phenomena. Peter Mair and Richard Rose advance a slightly different definition, arguing that comparative politics is defined by a combination of a substantive focus on the study of countries’ political systems and a method of identifying and explaining similarities and differences between these countries using common concepts.
Rose states that, on his definition: “The focus is explicitly or implicitly upon more than one country, thus following familiar political science usage in excluding within-nation comparison. Methodologically, comparison is distinguished by its use of concepts that are applicable in more than one country”.
Several different strategies can be used in comparative research.
i. Most Similar Systems Design/Mill’s Method of Difference: it consists in comparing very similar cases which only differ in the dependent variable, on the assumption that this would make it easier to find those dependent variables which explain the presence/absence of the dependent variable.
ii. Most Different Systems Design/Mill’s Method of Similarity: it consists in comparing very different cases, all of which however have in common the same dependent variable, so that any other circumstance which is present in all the cases can be regarded as the dependent variable.