ABSTRACT
The national statistics of developed countries make extensive use of standard classifications that are highly detailed, and the analyst may generate still finer distinctions and groupings from them. Theories, that are the basis of thought in demography, cannot be conceived without precise representation of the phenomena studied. In the Lexis diagram the mode of representing demographic events is systematized, where elapsed intervals (or ages, which are the intervals elapsed since birth) and dates are combined. In demography, events are generally observed over the calendar year. One thus speaks of births occurring at 7 years of marriage in complete years or during the 8th year of marriage. The scale of intervals and ages employed in demography may be large or small, depending upon the phenomena under study. The population is classified by age; legitimate births in a given year are classified by the duration of marriage of the parents or by the interval since the preceding birth.
