that in some societies the premature death of an adult is seen as a more significant event in the family than the death of a child, and that it may therefore be possible to use a longer recall period when questioning relatives about adult deaths. It may also be argued, however, that a mother may be more intimately involved in the care of a sick child, and therefore better able to give details of symptoms, than would a relative caring for an adult. This would suggest that a shorter recall period might be necessary in a study of adult deaths. In some cultures the first anniversary of a death is an event of great significance thus making the first year after a death a clearly defined period. Recall may also be more reliable in that period than subsequently if the period of mourning serves to keep the memory of the death fresh until the final rites are observed. Further research is clearly required on an appropriate choice of recall period for adult deaths.

Some causes of death, in particular external and maternal causes, do not require any knowledge of symptomatology. Consideration should therefore be given to the possibility of adopting less stringent criteria for recall period and proximity of residence for selected causes of death. This option is discussed further in Section 4.5

# 3.2.4 Sampling methods

A decision would be needed on the definition of the population of interest. This could be the entire population of a country, it could exclude urban areas if these were already well covered by vital registration, or could be restricted to some sub-national area. The sampling procedure would be chosen with the aim of giving a representative sample of the defined population.

Given the lack-of reliable sampling frames in most developing countries, some form of multi-stage sampling is the most likely alternative for a single-round survey. The basic approach would be to select communities with probability proportional to size, and then to sample a fixed number of households or persons in each selected community.

The required sample size needs careful consideration. It is considered that data would need to be collected on at least 200 deaths in order to provide reasonably accurate information on the proportions of deaths attributable to different causes. Assuming a death rate in adults aged 15-64 years of roughly 5 per thousand per year, it follows that a population of about 40,000 adults would be needed to produce 200 deaths in one year. If questioning were to be restricted to those living in the same household as the deceased, this would,mean visits to enough households to provide a total adult population of about 40,000. The number of households would thus depend on average household size. In a community with an average of two adult members per household, a sample size of around 20,000 households would be required. Demographic surveys using indirect methods typically require sample sizes of between 3,000 and 10,000 households, and this demonstrates that somewhat larger samples are likely to be needed if reliable data on cause-specific mortality are to be obtained. Even larger samples would be needed if detailed comparisons were to be made in patterns of cause-specific mortality between different age-groups or geographical areas.

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