The Basic Principles of research design of comparative research Morris zelditch(1971) specifies that the design of comparative research is conditioned largely by four rules Rule of one variable: No second variable u is definitely the cause or effect of v if there exists a third variable, w, that is present or absent in the same circumstances as U. In order to verify that U and v are correlated in the design where there are other 2 variables, say w and x, we need at least eight cases(2x2 a x2 )of the following natureThe Basic Principles of Research Design of Comparative Research Morris Zelditch (1971) specifies that the design of comparative research is conditioned largely by four rules: Rule of One Variable : No second variable U is definitely the cause or effect of V if there exists a third variable, w, that is present or absent in the same circumstances as U. In order to verify that U and V are correlated in the design where there are other 2 variables, say W and X, we need at least eight cases (2x2x2) of the following nature