Kachirayan (1983) reported a study of cause of death based on deaths registered in Madras, India in 1975 and 1976. Deaths taking place in hospitals, clinics and nursing homes accounted for 27% of all registered deaths, and these institutional deaths were the only ones investigated by cause. In the a-e--group 15-44 years, 1866 deaths were available for analysis. A second hospital-based study was reported by Williams et al (1986), who analyse' the rs-corded causes of the 1960 deaths occurring in a rural hospi ..al in West tzile District, Uganda during the period 1951-1378. Of these deaths, 679 were of "adults" aged 12 or over, but no data on exact age were recorded and so it was not possible to separate out deaths in adolescence or in old-age from those of adulthood. Both the Madras and the West Nile data are based entirely on hospital deaths, and so cannot be regarded as representative of causes of death in the general population.

One major study has been published that draws together information from a range of sources. The Ghana Health Assessment Project Team (1981) used census data, death certificates, hospital statistics and data from special studies and surveys to estimate the incidence, case-fatality and average age at onset of each cause. These are used to derive estimates of the person-years of healthy life lost from each cause. Data are given for all ages combined. However, rough estimates of cause-specific adult mortality rates may be obtained by restricting attention to those diseases with an average age at onset of 15 years or more, although of course some childhood deaths will be included and some adult deaths will be omitted through this procedure. No details are given of the exact sources of information, nor of the methods by which they have been combined, and it is unclear how reliable the data are likely to be on a national basis.

Finally, Grosse (1980) gives data for specific areas in Ghana, Pakistan, Indonesia and Nepal, but no details are given of the methods by which they were collected.

# 2.3 Methods of classification

Once data have been collected on the causes of deaths occurring in a defined population, these causes have to be classified into categories for the purpose of presentation. Several different methods of classification have been used in the data sources described above.

Vital registration data are generally presented according to the International Classification of Diseases (ICD). The ICD groups diseases under 17 main headings, each of which is broken down into a large number of categories, each given a 3-digit code. These categories are in turn divided into subcategories represented by a fourth and occasionally a fifth digit. A supplementary classification, consisting of 3-digit codes preceded by the letter "E', is available for external causes of injury and poisoning. Because of the very large number of 3-digit categories, data are often grouped for tabulation according to various abbreviated lists. The ICD is revised every 10 years, the most recent revision being the ninth (ICD-9), published in 1977. These revisions ensure that the classification develops in response to advances in medical science, although differences between the revisions add to difficulties of comparison. This is illustrated by differences in the classification of TB under the abbreviated B and AM lists of the eighth 6