Performance criteria for verbal autopsy-based systems to estimate national causes of death: development and application to the Indian Million Death Study

Abstract

Background: Verbal autopsy (VA) has been proposed to determine the cause of death (COD) distributions in settings where most deaths occur without medical attention or certification. We develop performance criteria for VA-based COD systems and apply these to the Registrar General of India's ongoing, nationally-representative Indian Million Death Study (MDS).

Methods: Performance criteria include a low ill-defined proportion of deaths before old age; reproducibility, including consistency of COD distributions with independent resampling; differences in COD distribution of hospital, home, urban or rural deaths; age-, sex- and time-specific plausibility of specific diseases; stability and repeatability of dual physician coding; and the ability of the mortality classification system to capture a wide range of conditions.

Results: The introduction of the MDS in India reduced the proportion of ill-defined deaths before age 70 years from 13% to 4%. The cause-specific mortality fractions (CSMFs) at ages 5 to 69 years for independently resampled deaths and the MDS were very similar across 19 disease categories. By contrast, CSMFs at these ages differed between hospital and home deaths and between urban and rural deaths. Thus, reliance mostly on urban or hospital data can distort national estimates of CODs. Age-, sex- and time-specific patterns for various diseases were plausible. Initial physician agreement on COD occurred about two-thirds of the time. The MDS COD classification system was able to capture more eligible records than alternative classification systems. By these metrics, the Indian MDS performs well for deaths prior to age 70 years. The key implication for low- and middle-income countries where medical certification of death remains uncommon is to implement COD surveys that randomly sample all deaths, use simple but high-quality field work with built-in resampling, and use electronic rather than paper systems to expedite field work and coding.

Conclusions: Simple criteria can evaluate the performance of VA-based COD systems. Despite the misclassification of VA, the MDS demonstrates that national surveys of CODs using VA are an order of magnitude better than the limited COD data previously available.

Figure 1

MDS flow of activities. To date, about 700,000 deaths have been surveyed and 200,000 deaths have been double coded. The eventual numbers covered will include about 350,000 deaths from 1997 to 2003, of which half will have used the RHIME instrument, and about 650,000 deaths from 2004 to 2014. MDS, Million Death Study; RHIME, routine, reliable, representative, resampled household investigation of mortality with medical evaluation.

Figure 2

Proportion of cause-specific neonatal deaths by age (days). These three conditions account for 80% of all neonatal deaths in India [12].

Figure 3

Proportion of cause-specific child deaths by age (1 to 59 months). Pneumonia and diarrhea account for 50% of all deaths in India at these ages [12]. *Other infections include sepsis, meningitis, encephalitis, tuberculosis, tetanus, polio, measles, HIV, malaria, other infectious and parasitic diseases, and fever of unknown origin.

Figure 4

Proportion of selected communicable and non-communicable deaths in adults by age (years).

Figure 5

Proportion of road traffic injury and suicide deaths in adults by age (years). Road traffic injuries are more common in men than in women [32], but suicide at younger ages is more common in women [16].

Figure 6

Seasonality patterns of snakebite mortality and rainfall in states with high-prevalence of snakebite deaths during 2001 to 2003. Rainfall amount (mm) is cumulative station-wise daily rainfall for the past 24 hours measured at 0830 IST of the day by the India Meteorological Department at its 537 observatories. Maximum and minimum temperatures are also measured daily on the same grid but not presented here. Temporal correlation between snakebite mortality and rainfall: 0.93 (P <0.0001), temperature minimum: 0.80 (P = 0.002), temperature maximum: 0.35 (P = 0.25) [17].