Much of this work explicitly or implicitly relies on the comparative method of analysis which Skocpol and Margaret Somers note are essentially of two forms: what they call the "Method of Agreement
" between two societies where the outcome is the same, but most institutions were different, and the "Method of Difference" where all but one of the causal factors or institutions were the same in two societies, and their outcome was different.
We faced three major analytical issues: the issue of representativeness, the inability to apply the logic of multivariate analysis, and the difficulty in applying Mill's (1967) method of agreement of method of difference.
That is why the causal reasoning we employed could not rely on Mill's method of agreement, and why it is highly interpretive.
Because political violence erupted in both Italy and West Germany, della Porta employs John Stuart Mill's method of agreement to discern variables that have explanatory power for political violence in each country.
As della Porta points out, the employment of the method of agreement may potentially limit her findings.