Modelling and prediction of global non-communicable diseases

Non-communicable diseases (NCDs)—namely cardiovascular diseases, diabetes, cancer and chronic respiratory diseases—have a higher morbidity and mortality rate globally than do all other causes combined [1]. They are the main health and development challenge facing humankind in the twenty-first century. They have caused certain damage to the socio-economic structure of human beings and countries, especially low- and middle-income countries (LMICs) [1]. The distribution of NCDs was mainly widespread in developed countries in the early years. However, the NCD incidence and mortality in LMICs have been increasing in recent years [2]. It is worth mentioning that in all continents, except Africa, the number of deaths from NCDs has now exceeded the total number of deaths from communicable, maternal, perinatal and nutritional conditions [1, 3]. The World Health Organization (WHO) estimates that by 2020, NCDs will account for 80% of the global disease burden. Seven out of every ten deaths in developing countries are caused by NCDs, and about half of these deaths are in people younger than 70 years [4‐7]. Moreover, the global NCD burden will increase by 17% in the next decade, and in Africa, it will increase by 27%. Nearly half of all deaths in Asia are attributable to NCDs, accounting for 47% of the global disease burden [4]. The International Symposium on “NCDs in Developing Countries” was held on 22 March 2014 at Ludwig-Maximilians-Universität in Munich, Germany, to discuss the direction of NCD control in developing countries [8]. This is an indication that developing countries are beginning to pay more attention to NCDs.

NCDs are a kind of “rich and noble diseases” in people’s conventional cognition. Their impact has been attracting attention in countries and regions with a high degree of economic development and a severely ageing population, and they are also a matter of significant concern internationally. Developed countries have been bearing the NCD burden from the early years, so they have accumulated more experience in the disease prevention and control. But, in recent years, people have discovered that NCDs are not just “rich and noble diseases”, and their impact on developing countries cannot be underestimated [9]. Developing countries and regions have not shaken off the impact of infectious diseases, and the NCD burden has increased rapidly [10]. Especially for LMICs and regions, NCDs have even become a barrier to their continued economic development and progress [11]. Ultimately, the mechanism of NCDs is inextricably linked with the influence of socio-economic factors, and the transition of human disease burden from infectious to non-infectious diseases has been driven by many factors indicating economic development [12]. It is just that the leading factors for and risks of NCDs in countries and regions at different economic development stages are different. The specific manifestations of human socio-economic development related to the occurrence of NCDs have the following major aspects: in terms of economy, increased financial capacity and increased disposable income [13‐17]; in terms of diet, the transition from traditional foods to high-fat, high-salt and high-sugar processed foods, with diet structure becoming unhealthy [17‐23]; in terms of work and lifestyle, because of the change in the type and nature of work and the increase in living pressure—coupled with changes in the type of daily recreational activities—people have become more sedentary and lack physical activity [16, 17, 24‐29]; and in terms of educational awareness, including alcohol and tobacco consumption and control [13, 20, 25, 26, 30‐40]. In addition, infectious diseases can be effectively controlled through medical means such as vaccines and drugs, but NCDs have no effective means of control because of their relatively complicated mechanism of action. Therefore, the proportion of NCD deaths will continue to increase [12]. Hence, whether in developed or developing countries, the NCD burden on human beings cannot be ignored.

This study also explores the changing trend of NCD deaths from the perspective of socio-economics, which is based on the study of socio-economic factors. Unlike previous studies, this study considers the stratified heterogeneity of socio-economic development as the entry point. The socio-economic development of different countries around the world does not necessarily follow the same path and laws, but different types show different development paths. NCD deaths are related to socio-economic development, so they may also show corresponding stratified heterogeneity. That is to say, the development trend of NCD deaths in different country types and development stages would also be different, whereas the same country types may show similar development laws. Exploring the change and development of NCD deaths on such a layered basis will get more accurate results than do ordinary global studies. The evolution tree model (Geotree) is a multidimensional visualization model with stratified heterogeneity as its core [41, 42]. The spatio-temporal evolution tree model is not limited by dimensions. By combining the development law of things, the mechanisms and evolution that may exist in multidimensional data are expressed in a simple and clear visual form [42]. In addition, the multilevel model (MLM) in Geotree is completely based on stratified heterogeneity for model fitting and predicting future changes in NCD deaths, which provides better accuracy than ordinary global models do. It is worth mentioning that Geotree not only has the results of quantitative analysis, but also covers the qualitative description, which makes it possible to explain the changing trend of NCD deaths mechanically.

In this study, the level of national income was selected as a classification indicator of the first branches of the NCD evolution tree. The level of income (or GDP) is one of the most direct factors for measuring a country’s economic development, and it is also a universal standard for international classification of countries. In the construction of the secondary trunks of the evolution tree, this study opted to use the level of urbanization and neonatal mortality as the calculation indicators, mainly because the development of urban areas and the improvement of medical conditions are also two important aspects to measure the social and economic development of a country. Some studies have found that, with the development of urbanization, the diet structure tends to be high in sugar, salt and oil, there is lack of exercise, and people tend to lead a sedentary life. Their average body mass index (BMI), blood lipids, blood pressure and other physical indicators also rise, eventually leading to the increased NCD incidence [57‐62]. As the main component of chronic diseases, NCDs are closely related to socio-economic development. Therefore, this study focused on the influence of socio-economic factors and combined the perspective of the evolution tree to explore the law of NCD deaths. In addition, an important feature of Geotree is “evolution”. The Geotree classification indicators selected in this study—such as the level of national income, urbanization rate and neonatal infant mortality rate—are all development indicators that measure a country’s level of development from three aspects: (i) economic, (ii) social and (iii) medical. The basic socio-economic factors are also easy to obtain, which is convenient for the subsequent evolution modelling of future NCD death index trends.

Moreover, the interpretation power of the two-level classification results of Geotree was also calculated using the Geodetector. The specific results are shown in Table 3. The q-values of the country types reached 0.45 (age-standardized NCD mortality rate) and 0.61 (NCD deaths of the total number of deaths), and both passed the significance test. It has been proved that the classification of the country type has a strong interpretation of the NCD death indexes.

The national socio-econamic development stage also maintained a high level of explanation for NCD mortality (with a q-value of 0.49, passed the significance test) and the proportion of NCD deaths to total deaths (with a q-value of 0.74, passed the significance test; Table 4).

Combining the results provided previously, it can be found that with the development of economy, no matter whether the level of income increases, or urbanization rate and medical level increase, the NCD mortality rate decreases with it. This shows that NCDs are effectively controlled with the level of socio-economic development. The improvement of the level of economic development allows more patients with NCDs to be able to afford the cost of treating the disease and choose to seek medical treatment [63], and the improvement of medical conditions allows NCDs to be effectively treated, and ultimately, the mortality rate is reduced.

In contrast, the proportion of NCD deaths to total deaths is increasing, which shows that with the development of economy, infectious diseases can be better controlled through the development of economy and improvement of medical conditions. However, the adjustment of industrial structure, change of lifestyle and change of dietary structure brought about by economic development will aggravate the NCD incidence and deaths. Studies have suggested that the occurrence of NCD will be more common in fast-growing cities with higher survival stress, fast-paced lifestyles, lack of exercise and rising air pollution [64‐66]. The increase in the proportion of NCD deaths to total deaths with economic development also proves that the mechanism of NCDs is more complicated.

From the perspective of the branch structure of the evolution tree combined with geographic space, the distribution of the four country types is roughly as follows: country type I (low-income economies), mainly distributed in Africa; country type II (lower middle-income economies), mainly distributed in Southeast Asia, South Asia, Central Asia, other Asian regions and a small part of Africa; country type III (upper high-income economies), located in East Asia, Latin America, West Asia and North Africa, but also includes parts of South Africa and a small part of southern Europe; and country type IV (high-income economies), mainly North America, Europe and a small part of Oceania. On the contrary, the regions with higher NCD mortality rate are countries with lower levels of economic development, mainly countries in Africa and some countries in Asia (Southeast Asia, South Asia, etc.). The regions with a higher proportion of NCD deaths to total deaths are developed regions such as North America and Europe. This also proves from the side that the NCD death indexes and level of economic development show a high correlation; that is, the NCD mortality rate and the level of economic development generally show a negative correlation, and the proportion of NCD deaths to total deaths and the level of economic development are roughly positively correlated.

Although the close relationship between NCDs and socio-economic development shows a positive or negative correlation as a whole, the leading factors for the occurrence of NCDs are different in countries and regions at different socio-economic development stages. In comparison, in less developed areas (such as country type I and II), the residents have higher levels of alcohol and cigarette consumption and start smoking at a young age (including second-hand smoke); even tobacco consumption by some poor families is equivalent to the dietary expenditures of one or two undernourished children [36, 66‐70]. These people also consume insufficient fruit and vegetables [16, 32, 66, 71‐73]. Moreover, they may develop NCDs because of some congenital factors or the induction of a harsh living environment, such as poor breastfeeding and being underweight during childhood [74]. In addition, because of the backward level of socio-economic development, fossil fuels account for a relatively high proportion in household use, such as heating and cooking, so household air pollution is also the cause of some kinds of NCDs [74]. In contrast, the residents in regions with high levels of socio-economic development (such as country type III and IV) display lack of physical activities and consume more high-oil and high-salt processed foods [66, 75‐77]. Therefore, in contrast to underdeveloped regions, NCDs caused by abnormal physical indicators (blood pressure, blood lipids, BMI, etc.) resulted from acquired dietary habits and living habits are the main part of NCD incidence [59]; this part also needs to be explored in future experiments.

In the MLM fitting experiment, an MLM and a general global linear regression model were used for fitting. From the calculation results, it can be seen that the prediction accuracy of the MLM is better than that of the general global linear regression model. This shows that there is hierarchical heterogeneity in the distribution of NCDs. If only the global linear regression model is used, although it is simple to calculate, it will ignore this characteristic, resulting in less accurate results than the MLM.

Regarding the current situation of non-communicable diseases gradually becoming popular in low- and middle-income countries and developing countries in recent years, governments of all countries in the world should pay sufficient attention and take effective measures to prevent the prevalence of non-communicable diseases. The government can spread the risk factors and prevention methods of diseases to the public by introducing more authoritative NCDs popularization and prevention measures, so as to arouse ordinary people’s higher attention. At the same time, vigorously carrying out public health monitoring and improving the health management system are also effective measures to prevent and control non-communicable diseases. Under the guidance of medical theory, through the establishment of health records to conduct a scientific analysis of the public’s health status, targeted expert advice and management programs are given. In addition, the evolutionary tree method can also be used to calculate the relationship between the level of socioeconomic development and NCDs distribution in different regions of a country. Based on the simulation results, the government can allocate medical resources and public health facilities in a targeted manner to improve the utilization of medical resources. Countries can also establish international organizations that collaborate in the prevention and control of diseases, learn from each other’s useful experience, and provide some assistance to countries with relatively backward medical standards to jointly contribute to the prevention and control of non-communicable diseases.

This article explores the distribution and evolution of NCD death indicators from the socioeconomic dimension. NCD deaths have obvious stratified heterogeneity, showing different distribution patterns in countries and regions with different social and economic conditions. The evolution tree model is a classification-based visualization method. Its core is stratified heterogeneity and the calculation process is not limited by the data dimension, which can cover as many factors as possible that affect the development of things. Exploring the distribution and evolution of NCDs death on a hierarchical basis can effectively control some confounding factors that exist in ordinary global studies and obtain more accurate results. And the perspective of this study is between macro and micro, which is more conducive to playing an important guiding role in the allocation of medical resources and the implementation of prevention and control measures. Moreover, countries with different levels of development can also have a higher reference value for their NCDs prevention and control by referring to the development and prevention measures of countries on the same branch and trunk as their own.

However, this study also has certain limitations. Limited to the lack of indicators of global socio-economic factors that use countries as statistical units, this article can only use common public data indicators to do the evolution tree classification, which to a certain extent weakens the advantages of the evolution tree’s multi-dimensional coordinate system. In the follow-up research, this is an aspect that needs to be improved. Enrich the types of indicators of social and economic factors as much as possible, so that the advantages of the evolution tree model can be better played, and the research results can be more detailed and comprehensive.

This study found that there is a clear correlation between socio-economic factors and NCD death indicators and that there is significant stratified heterogeneity in the distribution of NCD deaths. The construction of the spatio-temporal evolution tree model is based on a country’s recognition of its own level of NCD deaths, helping it to have a more comprehensive positioning of the characteristics of the NCD death indicator in the socio-economic dimension. By grading the branches of the evolution tree, different country types can find their place in the tree structure. Countries located on the same first branch belong to the same type. They have similar socio-economic conditions and similar development paths. Therefore, the development of secondary branches from the lower to higher stage on the same primary branch is the common development path of the same city types. By grading the branches of the evolution tree, different country types can find their place in the tree structure. Countries on the same branch belong to the same type, and the secondary trunks under each branch represent the development status at different stages. The socio-economic factors of the countries on the same branch are similar, and they generally follow the rule of development from lower secondary trunks to the higher ones; that is, they have similar development paths. When a country finds its own position in the tree-like coordinate system of the evolution tree, it can refer to the development direction of the country at a more advanced stage and combine its experience in disease prevention and control to locate its own development goals and formulate corresponding NCD prevention and control plans. Different country types can also learn from each other and take the road of NCD prevention and control in accordance with their own national conditions on the basis of their own characteristics.