This work was framed in a non-experimental transectional study, it presents a scheme for the determination of the most important or essential variables of a system. The variables are chosen through the use of three techniques, brainstorming for the collection of information, MICMAC for the determination of variables and time series as a second filter of key variables and analyzing their behavior. As a result, precision is obtained in the identification of the key variables of a system and their behavior by combining these techniques.