Introductory

The first part of this chapter will be concerned briefly with the biology of fertility (§ § 6.2, 6.3) and then the sections that follow will discuss the nature of the principal social and other factors which influence fertility from time to time (§§6.4–6.8). The remainder of the chapter will outline the various forms of statistical analysis with illustrative examples. Methods for use in analysis where the data available are scanty or untrustworthy will be outlined in chapter 19. It is probably true to say that the demographer never finds ready to hand all the statistics which might be desirable for a full study of the subject; but in the present chapter it is assumed that some reliable information at least is available, with perhaps a subdivision by at least one useful parameter.

Fertility becomes possible when adulthood begins, namely at ‘puberty’ (for girls the word ‘menarche’ is also used). Studies of the age of puberty show that it varies from country to country, and between the sexes, while it has also undergone marked changes from one century to another in recent times. It is more meaningful in statistical analysis to measure the number of births against the number of persons over the age of puberty than it is to express births as a proportion of population as a whole.

Fecundity and fertility

A woman's fecundity varies according to a monthly cycle, and study of this cycle is important in relation to the ‘rhythm’ method of birth control.