and ninth revisions respectively. Cases included under the TB classifications B5+6 and AM4 differ, in that the late effects of the disease are included in the B classification but not in the AM form. A comparison of TB deaths from the two classifications would therefore show an artefactual decrease in the latter.

An illustration of the difficulty of comparing data based on different classification systems is shown in Table 1, which presents vital registration data for the city of Belo Horizonte, Brazil. This table compares the classification of deaths of all ages under the PAHO ranking "R" list, the Brazilian mortality list ICI-BR, a newly proposed Brazilian list ICD-BRI, and the list of 72 causes of death of the National Centre for Health Statistics of the United States (NCHS). The ICD-BR and ICD-BR2 list give malignant neoplasms as the leading cause of death whereas the R and NCHS lists indicate heart disease as the leading cause. While most of the conditions mentioned in the leading ten causes of death appear on all the lists, diabetes and chronic liver disease are not represented in every case.

For data sources other than vital registration, numbers of recorded deaths are generally small, and broader groupings of causes are therefore needed for data presentation. The groupings adopted have varied widely between studies, partly because of variations in disease patterns between countries, but also because of differences in v data-collection methods. For example, if lay inter.iewers are rised to make a diagnosis, a highly detailed classificaticn system is less likely to be appropriate for data presentation. Differences in the classification systems used in different surveys add consiCerably to the difficulties in making comparisc-.s between countries and areas.

# 2.4 Summary of available data

Data from vital registration are presented first, followed by data from other sources. As discussed in Section 2.2, very few vital registration data on cause-specific adult mortality are available for the developing countries of Africa and Asia, although rather more are available for Latin America. Table 2 shows the leading causes of death in adults aged 15-64 years for Guatemala, Mauritius, Egypt, Thailand and Sri Lanka. All these countries, however, have considerably higher expectations of life at birth than the less developed countries that are the main focus of this paper, and it is possible that their patterns of cause-specific mortality are also different. The disease categories chosen for presentation in Table 2 are rather broad. This is necessary to allow comparisons between the five countries, as the level of detail in the reporting of data varies considerably from country to country.

Death rates in the age group 15-64 years in these five countries varied from about 3 to 6 per thousand per year. Circulatory diseases and external causes were the two leading causes of death in all the countries shown in Table 2 except Guatemala, wihere infectious and parasitic diseases were the leading cause, followed by external causes. The term "external causes" in this paper includes deaths from accidents, poisoning, suicide, homicide, and other violence. In Egy!)t, rheumatic heart disease accounted for a large proportion of deaths from circulatory diseases, especially in women. Pneumonia, other respiratory diseases and malignant neoplasms were also among the leading causes in 7