In developed countries, data on disease-specific mortality by age are readily available from national vital registration. In developing countries, the levels of coverage of vital registration and reliability of cause of death stated on the death certificate are generally low (especially in rural areas).
Reliable assessment of disease-specific mortality rates is not yet possible in many parts of India, either because the underlying cause of the terminal illness was never known or because the relevant information was not recorded. For legal purposes death records do usually subdivide the causes of death into medical and non-medical (external) causes. But once non-medical causes have been excluded, specification of the underlying cause of a death from disease may be inaccurate, misclassified or missing for about 50% of adult deaths.
This special study of verbal autopsy carried out in Chennai among 48 000 adults aged 25 and above at the time of death during 1995–97. Of the 25 000 male and female deaths at ages 25–69, 7000 took place in hospital, and for these the underlying cause should have been entered onto the death certificate by a hospital doctor. For the most of the remaining 18 000 deaths at these ages, the death certificate was obtained from a physician practicing near the deceased's place of residence and he might not have had a chance of treating the deceased when he/she was alive. So, for these deaths, the cause on the death certificate may well have been unspecified (41%). VA yields fewer unspecified causes (only 10%) than the death certificate, particularly for the deaths that did not occur in hospital, and often yields somewhat more specific information, eg. about the approximate site of origin of a cancer, or about evidence of tuberculosis, stroke, myocardial infarction or diabetes. In addition, the probable cause of death arrived by verbal autopsy allows subdivision into the broad groups of disease.
The validity of verbal autopsy may have depended on the training of the interviewer, on the immediate random checking of the 5% of interview data to assess the reliability and reproducibility of the procedures and on the availability of physicians to interpret the field reports to arrive at the probable underlying cause of death. In the present study, field reports were reviewed centrally by physicians to arrive at the probable cause of death; for those settings where physician review is not possible, algorithms provide an alternative approach for assigning cause of death [9
]. The cause of death arrived based on reviewing verbal autopsy reports by physicians is better than that arrived by opinion-based algorithm [10
In Chennai, registration of the fact of death is almost complete, as is the subdivision into medical and other causes but certification of the underlying cause of death is less reliable. A study done in Chennai [11
] showed that the sensitivity of the death certificate to identify cancer as the cause of death was 57%; in Chennai about 75–80% of cancer patients attend health care facilities at late stage of the disease; for about half of those who died at home soon after the diagnosis of cancer (and whose deaths were therefore, in almost all cases, likely to have been caused by their cancer) do not have cancer mentioned on their death certificate [11
], and for other diseases the problems might well be even worse. In the present study the sensitivity of VA to identify cancer deaths was 94% and there were no false positive cancer deaths. The high sensitivity seen in this study may be due to the ascertainment of data from the spouse (close associate) by the field interviewers on the type and duration of treatment received by the deceased for their illness and the name of the hospital (location of the hospital) and/ or name of the unit (eg. Cancer unit / Coronary Care Unit etc) where they were admitted for treatment. Most of the close associates of the deceased were aware of the diagnosis of the illness as told by the treating physician. Higher sensitivity of verbal autopsy suggests that there is less likelihood of over estimation of underlying cause of death. In this study wife appeared to be a better responder than husband. This may be due to the following reasons: wife remembers the circumstances that led to death of her spouse better than husband remembering his spouse's death because of more attention and care is given to the health of males in the community than of females in general.
About 80% of world's death occur in developing countries; but estimation of cause of death is more difficult in developing countries because of paucity of mortality statistics. Verbal autopsy of all adult deaths helped us to compute mortality rates for Chennai. Among infectious diseases death rate for respiratory tuberculosis was higher compared to other infectious diseases from 25–74 years among men and from 25–54 years among women. Among vascular diseases death rates from cardiovascular was higher in all age groups in both genders compared to death from stroke. Over all, the mortality rates in Chennai are higher than the rates in developed countries [12
]. However mortality rates for neoplasm and cerebrovascular diseases are lower and that for cardiovascular and respiratory diseases are higher in Chennai in the age group 35–69 compared to similar age group in developed countries in both genders. The mortality rates among males and females for tuberculosis in the early adult life and middle age in Chennai is about 14-fold and more than 20-fold higher, respectively, than the mortality rates in developed countries.
The strengths of the study are: 1. large sample size that included all deaths attributed to medical causes in a defined area to avoid selection bias, 2. open format used for verbal autopsy to collect data on all causes of death instead of restricting to few causes as in a structured questionnaire, 3. review of verbal autopsy reports centrally by 2 physicians, independently, to arrive at probable underlying cause of death and 4. validation of the field visit reports by re-interview of 5% of the collected data by special interviewers.