ABSTRACT
There are three main types of statistically measurable issue: The frequency of various values of one character at any time or place; The tendency of the values of one character to vary over a sequence of times and places; The relationships, associations, correlations, or contingencies between the various values of two or more characters. The issue consists in contrasting the distribution of two specified years whose distance in time is measurable. The inaugural conceptions already named are appropriate to the description of political and economic tendencies and relationships no less than in the description of single political and economic characters. They form a sufficient vocabulary even when two or more sets of variable characters are dealt with. Graphs or pictures help the initiated but little in realizing the comparative frequencies of merely qualitative differences. The appropriate graph is an area bounded by a polygon or curve, often called a periodogram or histogram.
