ABSTRACT
This chapter introduces the measurement of mortality by considering in detail the various kinds of mortality rate used by demographers. In Section 2.2 the crude death rate is described, and in Section 2.3 the calculation of age-specific death rates is illustrated. Section 2.4 then explains the rationale behind, and the difference between, two types of mortality rate commonly used by demographers: initial rates and central rates. These two types of rate are shown to be manifestations of two different approaches to analysing demographic data: that based on time periods; and that based on birth cohorts. Section 2.5 introduces the Lexis chart as a means of representing and illustrating the difference between initial and central rates, and thereby between the period and cohort approaches. In Section 2.6 the formula which is commonly used to convert age-specific death rates of one type into the other is derived, with the aid of a Lexis chart. Finally, Section 2.7 summarizes the advantages and disadvantages of the two types of mortality rate.
