This text has been written thinking fundamentally of the researchers of the different branches of science who work in one way or another to improve the life of man. In order to achieve their purposes they explore possible relationships between characteristics and properties present in the different phenomena that are the object of their research. In this study of characteristics and properties of phenomena, variables are defined. In the second chapter the variables are defined, always focused in the context of scientific research. In order to know the possible links between variables, correlation coefficients are studied, they provide different indicators with which the level of dependencies that may exist between variables can be measured. Precisely the correlation coefficients constitute the fundamental object of the Bivariate Correlation Analysis.