[1][2] They are intended to establish a causal relationship between two or more groups of data, analyzing their respective differences and similarities.
This method is also referred to more generally within comparative politics as the most different systems design.
Symbolically, the method of agreement can be represented as: To further illustrate this concept, consider two structurally different countries.
One factor that both countries have in common, the dependent variable in this case, is that they have a system of universal health care.
Comparing the factors known about the countries above, a comparative political scientist would conclude that the government sitting on the centre-left of the spectrum would be the independent variable which causes a system of universal health care, since it is the only one of the factors examined which holds constant between the two countries, and the theoretical backing for that relationship is sound; social democratic (centre-left) policies often include universal health care.
For instance, suppose that various samples of water, each containing both salt and lead, were found to be toxic.