The main purpose of our study is the establishment of the design manipulation on effective work groups which are fomed by the use of some sets of similar entities, i.e. "similar types of entities." Then a rational method to construct the similar types of entities and a new factor for dealing with these similar types as a variable are indispensable for it. This paper states the meanings of the "MC factor" which is introduced as the new factor, and a construction procedure of the similar types of entities is suggested as a way to determine the MC factors.