A vital statistics system is defined as “the total process of (a) collecting information by civil registration or enumeration on the frequency of occurrence of specified and defined vital events, as well as relevant characteristics of the events themselves and of the person or persons concerned, and (b) compiling, processing, analysing, evaluating, presenting and disseminating these data in statistical form.” (United Nations 2001: 3). Variants of a vital registration system include the Indian Sample Registration System (SRS), which seeks to record all events only in defined parts of the country. Furthermore, data from vital registration systems in developing countries are often substantially incomplete, and may be differentially incomplete by age and sex of the decedent. In such situations, direct estimation of mortality statistics using such data might produce severe underestimates of mortality.

A Population Register seeks to maintain a continuous record of the population size and demographic characteristics by updating a master list automatically every time a new birth or death is registered. When combined with other administrative systems – e.g. registration for employment, schooling or for taxation purposes – a population register can provide a detailed breakdown of the population at any given date, by age, sex, residence and other characteristics. Given the complications of maintaining and updating and automating such systems, they are comparatively rare – even in developed countries.]

A census may provide information on child and adult mortality. Direct estimates of adult mortality can be gained from reports of deaths in the household over the year preceding the census. The census results could also provide an updated estimate of the denominator for use with numerators derived from a vital registration system for the year centred on the census date to derive mortality rates. Indirect estimates of child mortality can be derived from women’s reports of their children born and surviving. Indirect estimates of adult mortality can be derived from answers given on parental or sibling survival. Both direct and indirect methods of mortality estimation rely on several strong assumptions and require significant assumptions and manipulations to derive reliable estimates. Their use is described in another Manual (Moultrie, Dorrington, Hill et al.. 2012)

Since mortality is a comparatively rare event in most human populations, sample surveys have to be formidably large to collect sufficient data of sufficient accuracy to estimate mortality (and especially the number of events in the numerator) accurately. In addition, since the sampling frame of many surveys is drawn from that of a national census, the denominators should have a similar distribution to those in the data from which the sample has been drawn, and hence errors in the underlying sampling frame, for example differential enumeration of the population in different regions, will carry through to the sample frame for the survey.