Everyone knows of the existence of intelligence tests. This is, in fact, the only aspect of applied psychology that is familiar to the general public. However, not so many people know that these tests have been the object of protracted studies and are integrated into a highly mathematized conceptual system. Our intention is to give a summary outline of this area of research which attempts to analyze man's performance, particularly in the area of the intellect.

The normal process of thought is to go from the concrete to the abstract. Therefore it seems natural to base this outline on an actual example of research carried out in the domain of intelligence and motor co-ordination tests and to use these as a point of departure for more general principles. In the first place, the material used—the actual tests—has a history that is in itself revealing. Second, the method of analysis employed is also deserving of study because it implies a certain number of postulates that must be understood in order to interpret the results it makes possible. Let us familiarize ourselves, then, with a typical factor analysis like the one made at the University of Neuchâtel in 1956.