Marriage and divorce rates are measures of the propensity for the population of a given area to become married or divorced during a given year. Some of the rates are quite simple, and others are progressively more refined. The simple ones are called crude rates and are expressed in terms of the number of marriages or divorces per 1,000 persons of all ages in the area at the middle of the year. These are the only marriage and divorce rates available for every state in the United States. They have the weakness of including in the base not only young children but also elderly persons, who are unlikely to marry or become divorced. But the wide fluctuations in crude rates over time are obviously associated with changes in the economic, political, and social climate.

More refined rates will be discussed below, but the...