Estimating population cause-specific mortality fractions from in-hospital mortality: validation of a new method

Abstract

Background: Cause-of-death data for many developing countries are not available. Information on deaths in hospital by cause is available in many low- and middle-income countries but is not a representative sample of deaths in the population. We propose a method to estimate population cause-specific mortality fractions (CSMFs) using data already collected in many middle-income and some low-income developing nations, yet rarely used: in-hospital death records.

Methods and findings: For a given cause of death, a community's hospital deaths are equal to total community deaths multiplied by the proportion of deaths occurring in hospital. If we can estimate the proportion dying in hospital, we can estimate the proportion dying in the population using deaths in hospital. We propose to estimate the proportion of deaths for an age, sex, and cause group that die in hospital from the subset of the population where vital registration systems function or from another population. We evaluated our method using nearly complete vital registration (VR) data from Mexico 1998-2005, which records whether a death occurred in a hospital. In this validation test, we used 45 disease categories. We validated our method in two ways: nationally and between communities. First, we investigated how the method's accuracy changes as we decrease the amount of Mexican VR used to estimate the proportion of each age, sex, and cause group dying in hospital. Decreasing VR data used for this first step from 100% to 9% produces only a 12% maximum relative error between estimated and true CSMFs. Even if Mexico collected full VR information only in its capital city with 9% of its population, our estimation method would produce an average relative error in CSMFs across the 45 causes of just over 10%. Second, we used VR data for the capital zone (Distrito Federal and Estado de Mexico) and estimated CSMFs for the three lowest-development states. Our estimation method gave an average relative error of 20%, 23%, and 31% for Guerrero, Chiapas, and Oaxaca, respectively.

Conclusions: Where accurate International Classification of Diseases (ICD)-coded cause-of-death data are available for deaths in hospital and for VR covering a subset of the population, we demonstrated that population CSMFs can be estimated with low average error. In addition, we showed in the case of Mexico that this method can substantially reduce error from biased hospital data, even when applied to areas with widely different levels of development. For countries with ICD-coded deaths in hospital, this method potentially allows the use of existing data to inform health policy.

Figure 1. Proportion of HIV/AIDS Deaths That Were in Hospitals, versus Age Group, According to Community Literacy Quartiles, Mexico 1998–2005

Data are means and 95% confidence intervals.

Figure 2. Proportion of Diabetes Deaths That Were in Hospitals, versus Age Group, According to Community Literacy Quartiles, Mexico 1998–2005

Data are means and 95% confidence intervals.

Figure 3. Proportion of Cerebrovascular Disease Deaths That Were in Hospitals, versus Age Group, According to Community Literacy Quartiles, Mexico 1998–2005

Data are means and 95% confidence intervals.

Figure 4. Proportion of Road Traffic Accident Deaths That Were in Hospitals, versus Age Group, According to Community Literacy Quartiles, Mexico 1998–2005

Data are means and 95% confidence intervals.

Figure 5. Average Relative Error in Population CSMFs when Based on Hospital CSMFs by State versus the Proportion of All Deaths Occurring in-Hospital, Mexico 1998–2005

Each point represents a state in Mexico. Legend: Ags, Aguascalientes; BC, Baja California; BCS, Baja California Sur; Camp, Campeche; Chih, Chihuahua; Chis, Chiapas; Coah, Coahuila de Zaragoza; Col, Colima; DF, Distrito Federal; Dgo, Durango; EDOMEX, Estado de Mexico; GRo, Guerrero; Gto, Guanajuato; Hgo, Hidalgo; Jal, Jalisco; Mich, Michoacan de Ocampo; Mor, Morelos; Nay, Nayarit; NL, Nuevo Leon;Oax, Oaxaca; Pue, Puebla; Qro, Queretaro de Arteaga; QRoo, Quintana Roo; Sin, Sinaloa; SLP, San Luis Potosi; Son, Sonora; Tab, Tabasco; Tamp, Tamaulipas; Tlax, Tlaxcala; Ver, Veracruz-Llave; Yuc, Yucatan; Zac, Zacatecas.

Figure 6. Population CSMFs Average Relative Error for 45 Cause Groups

ARE was calculated as a function of the percentage of Mexican VR data used to assess the proportion of deaths in each age, sex, and cause group dying in hospital.

Figure 7. Population CSMFs Average Relative Error for the Three Least-Developed Mexican States

Average relative error was estimated on the basis of the proportion of in-hospital deaths by age, sex, and cause groups observed in Distrito Federal and Estado de Mexico.