The manner in which the individual data items are arranged is of significance for two reasons. First, by appropriate arrangement the person attempting to interpret the data may obtain at least a subjective impression of the existing situation. Second, the manner of arrangement controls to a certain extent the computational procedures which are to be used in the analysis of the data. As a matter of fact, the data may have to be put into specific arrangements before certain parameters or statistics can be determined. Consequently, attention must be paid to how the data are arranged.