construction of this table, but a PYLL analysis could in principle be conducted for adult deaths only. Intestinal infections were the leading cause of death in terms of PYLL. From column 2, PYLL per death, it is clear that the majority of these deaths occurred in children. Cerebrovascular and ischaemic heart disease, which ranked highly according to proportionate mortality, appear less important in terms of PYLL becaase deaths from these causes occur later in life. Among adults, external causes were associated with the greatest number of years lost per death (about 40 per death), irinicating that such deaths are relatively common in young adults. Neoplasms ranked highly in terms of both PYLL and proportionate mortality. The number of years lost per death (about 19) was relatively low, but deaths from this cause occurred with great frequency.

The second example, from Ghana, is based on days of life lost per thousand per year, and has been constructed from data published by the Ghana Health Assessment Project Team (1981). The team used life tables for Ghana to establish the potential remaining years of life from the average age of onset of each cause. Estimates of days of life lost have been calculated by multiplying the published estimates of "days of healthy life lost" by the percentage of these days attributed to premature mortality. Only causes of death with an average age of onset of 15 years or more have been included In Table 9. Accidents again appear as the leading cause of adult death in terms of days of life lost, closely followed by TB.

A possible difficulty with rankings based on proportionate mortality and PYLL is that they are affected by the age structure of the population. In a population wit}h a rapid rate of growth, the population in younger age-groups will be much greater than in older age-groups, and this will be reflected in the numbers of deaths occurring in these age-groups. Thus it is possible to envisage a situation in which accidents appear as the leading cause of death on the basis of proportionate mortality or PYLL, but in which any given individual is more likely to die from, say, heart disease than from an accident. One approach which avoids dependence on the age structure of the population is to work in terms of the index 5oq-5, which represents the probability of dying by age 65 for an individual that has survived to age 15. Causes of death could be ranked according to their proportional contribution to this index.

# 5.0. RECOMMENDATIONS FOR FURTHER RESEARCH.

It should be clear from preceding sections that if,single-round surveys, using retrospective interviewing of relatives of the deceased, are to be implemented on a wide scale to obtain useful and comparable data on causes of adult mortality for a range of developing countries, a considerable amount of theoretical and methodological work will be needed to develop effective survey methods. Various aspects of this work are summarised briefly in this section.

Various sources of bias associated with variations in the probability of a death being reported, resulting from a survey approach based on the questioning of surviving relatives, have already been reviewed. These biases, and measures to reduce them, require further 26