The methods used to calculate the under-five mortality rate (U5MR) depend on the type of data available. In practice, data can be obtained from vital registration systems, sample registration systems, national population censuses, and/or household surveys. When data collected via vital registration systems is of good quality, the U5MR can be directly estimated by observing the survival status of different cohorts along time and to specific ages since the moment of birth. U5MR can be derived from household survey data using direct or indirect methods.
The direct method uses data collected on birth histories of women of childbearing age and produces the probability of dying before age five for children born alive, among women of childbearing age, during five year periods before the survey (0-4, 5-9, etc.). Direct methods require each child’s date of birth, survival status, and date or age at death. This information is typically found in vital registration systems and in household surveys that collect complete birth histories from women of childbearing age. Birth histories include a series of detailed questions on each child a woman has given birth to during her lifetime, including the date the child was born, whether or not the child is still alive, and if the child has died, the age at death.
The indirect method uses the Brass method, named after its original developer, William Brass, which converts the proportion of dead children ever born reported by women in age groups 15-19, 20-24,… 45-49 into estimates of probability of dying before attaining certain exact childhood ages. Brass’s method assumes that the age of the mother can serve as a proxy for the age of her children and thus for how long they have been exposed to the risk of dying.
Indirect methods require less detailed information that is available in censuses and general surveys, including the total number of children a woman has ever borne, the number who survive and the woman’s age (or the number of years since she first gave birth). However, indirect methods require model life tables to adjust the data for the age pattern of mortality in the general population. Finding an appropriate model life table can be challenging, since the Coale and Demeny model life tables are derived largely from the European experience.
Different data sources and calculation methods often yield widely differing estimates of child mortality for a given time and place. In order to reconcile these differences, UNICEF developed, in coordination with WHO, the WB and UNPD, an estimation methodology that minimizes the errors embodied on each estimate and harmonize trends along time. Since the estimates are not necessarily the exact values used as inputs for the model, they are often not recognized as the official U5MR estimates used at the country level. However, as mentioned before, these estimates minimize errors and maximize the consistency of trends along time. Applying a consistent methodology also allows comparisons between countries, despite the varied number and types of data sources.
After plotting all available values for infant and under-five mortality, analysts use weighted least squares to fit a multi-spline regression line to the data points and extrapolate the trend to the present. The use of weights allows analysts to make a judgment about the relative quality of each data set and how representative it is likely to be of the population. The last step is to decide which set of estimates (infant mortality or under-five mortality) is more consistent and to use a model life table to derive the other set of estimates from it.
Additional details of the methodology are available in the following working paper: UNICEF, WHO, The World Bank and UN Population Division, ‘Levels and Trends of Child Mortality in 2006: Estimates developed by the Inter-agency Group for Child Mortality Estimation’, New York, 2007: http://mdgs.un.org/unsd/mdg/Resources/Attach/Capacity/Ind%204-1.pdf
||These agencies have created the Inter Agency Group for Mortality Estimation (IGME).
||This methodology is better described in: K. Hill, R. Pande and G. Jones, Trends in child mortality in the developing world: 1990 to 1995, UNICEF staff working papers, Evaluation, Policy and Planning Series, UNICEF, New York, 1997.