Demographic and Health Surveys Methodology - Measure DHS

Because of the number of assumptions that may or may not hold, but that need to be made to use theindirect methods and the limited amount of information that they provide, DHS has chosen to use directestimation methods. There are three variants of direct estimation methods for estimating infant mortalityrates and other rates:1. A vital statistics approach in which the numbers of deaths to children under age 12 months in aparticular period are divided by the numbers of births in the same period. What is estimated is a rateof mortality but not a probability; a variation in the number of births with time will change the ratewithout changes in the underlying probabilities. To correct this, separation factors would need to beused, which would have to come from the other variants.2. A true cohort life table approach in which deaths to children under age 12 months of a specificcohort of births are divided by the number of births in that cohort. This procedure gives trueprobabilities of death, but has the drawback that all children in the cohort must have been born atleast 12 months before the survey to be fully exposed to mortality, thus not taking into account themost recent experience. This requirement of full exposure becomes more limiting the higher the agesegment of interest: For under-five mortality rates, only the information on children born five ormore years before the survey can be utilized. Another drawback is that true cohort rates are notspecific to a particular period at death, but instead relate to the date of birth of the cohort. Thereforethe effects of events that affect several cohorts at the same time, for example, a famine appears to bespread out over time.3. A synthetic cohort life table approach in which mortality probabilities for small age segments basedon real cohort mortality experience are combined into the more common age segments. Thisapproach allows full use of the most recent data and is also specific for time periods. It is themethod that the DHS has chosen to use.In this latter approach, there are still a couple of decisions to be made: the length of the individual agesegments, how to handle the heap of deaths at 12 months, and deaths with incomplete information on ageat death. The information on age at death is recorded on the DHS questionnaire in days for less than 0–30 days, in months for 1–23 months, and in years for two years or higher. The DHS adopted the followingage segments 0, 1–2, 3–5, 6–11, 12–23, 24–35, 36–47, 48–59 months (completed ages) for the calculationof the individual probabilities of dying. A different approach could have been to use monthly segments upto two years. This approach would have required much more computer memory, and studies done duringthe World Fertility Survey have shown the difference to be negligible. No adjustment for heaping on ageat death 12 months was done for the rates presented in the survey reports. Because heaping is likely tocome unequally from both sides of the one-year boundary and the correct number of deaths to reallocateis unknown, the rates are presented using the information as reported. Indeed, the extent of rounding upprobably varies by country and within country, and in some cases all or most of the heaping may be dueto reporting only whole year ages for children dying in the second year of life (rounding down ortruncation of age). For children with missing information, the ages at death have been assigned accordingto a “hot deck” technique in which the information of the child of the same birth order and form ofreporting (day, month, or year), if available, that precedes in the data file is assigned to the child forwhom age at death is missing. This is a quasi-random technique that preserves the variance of responsesin the data set.Guide to DHS Statistics 91 Updated September 2006