Analysis of lifetime death probability for major causes of death among residents in China

The age-specific mortality rate from 1st January 2004 to 31st December 2005 was sourced from the findings of the Third National Death Cause Survey [16]. This survey covered 213 counties across China and was hosted by the Ministry of Health of the People’s Republic of China. The age-specific mortality rates for 2014 were extracted from the Chinese National Death Cause Monitoring Dataset [2]. This dataset was compiled by the National Health and Family Planning Commission of the People’s Republic of China using 605 national disease surveillance system monitoring stations. China has used these two systems, the survey findings and dataset, for decades to provide nationally representative data on health status to guide health-care decision-making and performance evaluation. However, these systems overlapped to a considerable extent, entailing a duplication of effort. In 2013, the Chinese Government combined these two systems into an integrated national mortality surveillance system. This system provides a provincially representative picture of total and cause-specific mortality with which to accelerate the development of a comprehensive, nation-wide, system for vital registration and mortality surveillance. This new system increased the Chinese surveillance population from 6 to 24% [17].

Malignancy (C00-C97), cerebrovascular disease (I60-I69), heart disease (I05-I09, I10–13, I20–25), respiratory disease (J30-J98) and injury and poisoning (V01-Y89) were classified using the International Classification of Diseases, 10th revision (ICD-10) (WHO, 1992).

Based on the probability additive formula [12, 14], an abridge life table [9] was used to calculate the LDPs for the five leading causes of disease. The series of formulas is as follows:

q is the death probability. Subscript x and superscript i are indicator variables representing the age group and cause of death, respectively. D is the number of deaths. m is the mortality rate. r is the proportional mortality. d and l designate the death toll and survival number, respectively, in the life table. w is an indicator variable representing the oldest age group. \( {P}_0^i \) of age group 0 is an individual’s LDP [8].

China is a vast country with varying socioeconomic development status in different regions. Furthermore, trends in mortality and disease burden differ significantly at a provincial level. To facilitate the identification of health priorities at a regional level, we calculated the region-specific lifetime death probabilities for the first five major causes of death [3]. According to the National Bureau of Statistics, China can be divided geographically into three regions: the eastern, central, and western regions [14]. The eastern region includes the following municipalities and provinces: Beijing, Tianjin, Hebei, Liaoning, Shanghai, Jiangsu, Zhejiang, Fujian, Shandong, Guangdong, and Hainan; the central region includes Heilongjiang, Jilin, Shanxi, Anhui, Jiangxi, Henan, Hubei, and Hunan; and the western region includes Inner Mongolia, Guangxi, Chongqing, Sichuan, Guizhou, Yunnan, Tibet, Shaanxi, Gansu, Qinghai, Ningxia, and Xinjiang.

Although malignancy was the most common cause of death, the probability of death due to malignancy in a person’s lifetime was lower than that due to cerebrovascular and heart disease, the second and third most common causes of death in 2014, respectively. This phenomenon could be due to the differences in mortality rate between the diseases in certain age groups. The mortality rate of malignancy (54/100,000 population) was more than two times higher than that of cardiovascular (20/100,000 population) and cerebrovascular disease (21/100,000 population) at the age of 40–45 [2]. However, at the age of 80–85, the mortality rate of cancer (1266/100,000 population) was much lower than that of cardiovascular (2066/100,000 population) and cerebrovascular disease (2140/100,000 population) [2]. In the presence of competing risks, the events of interest are excluded by different events that had occurred previously [18]. Suppose now that the event of interest is the onset of “given disease”. Individuals may die without developing the “given disease”. We may then be interested in the risk or probability of getting the disease in a given follow-up period [5]. Calculation of the mortality rate is based on observed population without the disease as “independent censoring”, that is, a purely hypothetical population where individuals could not die without the disease. LDP is a much more satisfactory indicator, where one acknowledges that individuals may die without the disease and where inference for disease risks and rates are made “in the presence of the competing risk of dying”. In terms of age-specific mortality, those who died of cancer were younger, but those who died of cardiovascular and cerebrovascular diseases were older. On the surface, the mortality rate of malignancy is higher than that of cardiovascular and cerebrovascular diseases when not considering competing risks. The competing risk of death may be partly responsible for the observed difference between mortality rates and the LDPs. Furthermore, another important contributor is likely to be the current age structure of the Chinese population, which will influence the average mortality rate, but not the LDP. Therefore, we should consider the impact of competing risks and the age structure when assessing the severity of the disease. In this study, when formulating disease prevention policies, we should not only focus on the prevention of tumors, but also on the prevention of cardiovascular and cerebrovascular diseases.

Compared to 2004–2005, we found the LDPs from heart disease and malignancy increased in 2014, while the LDPs for respiratory disease and injury and poisoning in a person’s lifetime decreased. The Chinese government at all levels has actively promoted prevention measures to effectively control major risk factors in recent years. Respiratory disease, cerebrovascular disease and injuries and poisoning have declined, but heart disease and malignancy are still increasing [19]. These changes may require an integrated government response to improve primary health care and address key risks for heart disease and malignancy. To curb the increasing trend in chronic diseases (e.g. heart disease and malignancy), the Chinese central government has launched the initiative “Medium-to-Long Term Plan of China for the Prevention and Treatment of Chronic Diseases (2017–2025)” in 2017 [20]. Recommended prevention strategies include promoting health education, enforcing early diagnosis, reinforcing standardized treatment, strengthening the cooperation between health organizations, reforming healthcare policies, and improving chronic disease surveillance.

In this study, we found that the LDPs for the top five leading causes of death varied by regions. Across the eastern, central and western regions, malignancy had the highest LDP in the eastern region, cerebrovascular and heart diseases in the central region, and respiratory diseases, and injury and poisoning in the western region. A wide range of factors may contribute to the differences between regions including different lifestyles, eating habits, geographical locations, living environments, socioeconomic status, availability of medical resources, and access to medical screening and treatment. The eastern region is well developed, with a faster working pace and greater work pressure than other two regions, and possibly increased medical access to screening and treatment for cancer [21‐23]. It is of great importance in etiology and public health to explore the generality and characteristics of interregional disease incidence and mortality.

Factors contributing to obesity include rapid economic development and urbanization process, and unhealthy diets and lifestyles. Obesity is associated with heart disease and cerebrovascular disease [24, 25]. Proposed mechanisms linking obesity to cardiovascular and cerebrovascular disease include insulin resistance and chronic subclinical inflammation [26]. In recent years, the prevalence for obesity in the central region has been on the rise and increasing at a faster rate than the rate in eastern and western regions [27]. This could explain why the number of hypertension cases and deaths from hypertensive diseases are significantly higher in the central region than in the eastern and western regions [28]. In contrast, the LDP for respiratory disease was the highest in the western regions compared to the other regions. Relatively speaking, the western region has a lagging economy small population, and poor and uneven distribution of medical resources. The common use of indoor coal may be a causative factor for the high mortality rates from respiratory disease in this region [29‐31]. In addition, a higher smoking rate may also contribute to the higher LDP in the western region compared to other two regions [32].

In this study, we used LDP as an indicator to estimate the death probability for the top five leading causes of death. Compared to cumulative mortality rate and cumulative mortality risk, LDP has its advantages. Firstly, LDP can calculate the probability of death in one’s lifetime by using a probability addition model. However, cumulative mortality rate or cumulative mortality risk only be calculated for a specific age range (usually 0–74 years old) by using a probability multiplicative model. Secondly, LDP, based on the abridged life tables, is not affected by population composition [12]. Finally, LDP is a satisfactory indicator, where inference for disease risks and rates are made “in the presence of the competing risk of dying”. Although cumulative mortality rate or cumulative mortality risk can indicate the severity of a certain death cause, they do not take into account the existence of multiple causes of death. Therefore, LDP may be a more appropriate statistical indicator for situations where multiple causes of death and competing risks could be considered.

This study has potential limitation, and caution should be exercised in interpreting the results. The number of mortality monitoring points in China increased from 213 in 2004–2005 to 605 in 2014, which may affect the consistency in estimating the age-specific mortality rates. Nevertheless, in 2013 the National Health and Family Planning Commission combined the vital registration system and the disease surveillance points system to create an integrated national mortality surveillance system [2]. As the two mortality surveillance systems were similar in disease coding and classification, sampling method, and regional divisions, the age-specific mortality rates between 2004 and 2005 and 2014 should be comparable.