The ability of a nation to expand in the future is deeply dependent on its current quality of child care [1]. The quality of caregiving and structural measures has implications for children’s social, cognitive, and language development [2], but these factors are strongly affected by poverty [3]. About half of the world’s children have experienced extreme poverty, and most children have encountered various dimensions of poverty during their life [4]. Children from low-income and some middle-income countries experience deficient health care facilities, education, and other fundamental services in comparison with those of high-income countries. This can lead to the burdens of stunting and malnutrition, as well as higher rates of other morbidities and mortality [5].

Throughout the world, the physiological patterns of morbidity and mortality are consistent, but differences across countries in health systems and socioeconomic conditions can shape individuals’ health [5]. Consequently, a poor supply of medical technologies, low coverage of health services, malnutrition, overcrowding, indoor air pollution, poor hygiene and sanitation, and geographical variation lead to discrepancies in health and life expectancy [6]. For instance, children who have a healthy lifestyle will be more likely to be healthy and to engage in healthy behaviors [7], which can prevent illness, promote health, and prolong the life of people, including children [6]. Thus, children from developed countries have access to advanced health systems and modern medical technologies, which promote their health and longevity [4]. Nevertheless, in developing countries, the majority of children are distant from modern health care systems and their fundamental health rights are not guaranteed [8]. Therefore, children in these circumstances are more vulnerable to morbidity, disability, and mortality due to a lack of basic fundamental health services [5]. Additionally, children from developing countries have a 16 times lower likelihood of reaching their fifth birthday as compared to children from developed countries [8]. In developing countries, 12.7 million children died in 1990, a number that decreased to 4.8 million in 2015. In sharp contrast, however, only 1.1 million child deaths occurred in developed countries [4,9,10]. These huge differences in child mortality between developed and developing countries are essentially due to persistent disparities in health equity and health care facilities [4,10].

Numerous studies have been conducted across the globe in order to identify demographic and regional trends and patterns of child mortality using different statistical tools and techniques [11,12]. The reliability of these techniques is improved if countries have complete vital registration and demographic data [13]. However, most developing and even developed countries do not have accurate and reliable demographic data due to poor functioning of the vital registration and demographic surveillance system [12,14]. Thus, there may be differences between estimated trends and patterns of childhood mortality and the actual trends, and it may be difficult to make accurate estimations [12,13]. Although it is challenging to collect reliable and complete census and demographic data for many countries [12,14], the US Census Bureau provides accurate and valid population data for more than 192 countries [15]. These stable population data provide better insights into estimations of trends and patterns in mortality rate of children, and even for the adult population if migration from a given country is negligible [16]. In this regard, estimating child mortality from population data would be beneficial for countries lacking complete records of births, deaths, and other vital data, which impedes an understanding of mortality in under-5 children and its patterns and trends. Furthermore, this estimation of child mortality also plays a crucial role in preventing and controlling child mortality, particularly in developing countries, is highly important for achieving the targets set by the Sustainable Development Goals (SDGs) [4]. Therefore, the findings of this study can contribute to the effectiveness of programs for controlling the mortality rates in specific countries and motivate policy-makers and program implementers to shift the focus of programs from raising general awareness to provide other essential information. Additionally, it will help to develop flexible strategies to meet future needs for constructing healthcare facilities and services to deliver improvements in health among the vulnerable population of both developed and developing countries. Therefore, this study aimed to estimate under-5 child mortality in 52 low-migration countries using large-scale population data from the US Census Bureau.

This study utilized population data from the US Census Bureau from 1990 to 2015 [15]. In total, 52 low-migration countries were selected for this study, with 21 in Africa, 19 in Asia, and 12 in the West. These regions were grouped according to geographical boundaries and the pattern of mortality rates for each country. It has been well documented that most African countries share similar patterns of birth rates and death rates, while Asian and Western countries have different patterns [8]. Moreover, countries from each region (Africa, Asia, and the West) have similar patterns of fertility and mortality rate [16]. Therefore, this study aimed to estimate the mortality rates of under-5 children from the population data using a simple method based on the stable population data of children. Specifically, to estimate the age-specific mortality rates of under-5 children, we applied:

In this equation, N(x, t) is the number of children aged x in year t and N(x+1, t+1) is the number of children aged x+1 in year t+1.

The method first estimated the mortality rate based on the assumption of a low migration rate for each country, which was estimated by minimizing the values for all years (1990 to 2015). It was found that the data from 1990 to 2015 gave results that needed smoothing, and better results were obtained by selecting a few years. Thus, in this study, we only selected data from 1991, 1992, 1995, 1996, 2000, 2001, 2005, 2006, and 2008-2015, and a cubic root scale was applied to obtain better results. Consequently, single-year age groups from 1 to 5 years were used and the mortality rates of the 52 countries were calculated based on assumption of low migration. The selected countries, for which it was assumed that the net migration rate per 100,000 population was low in 2010-2015, are shown in Table 1 [17]. Additionally, children were grouped by age at 1-year intervals from 1 to 5 years, and the mortality rate per 100,000 live births was estimated. The US Census Bureau granted us permission to use their data, which are freely available from the US Census Bureau website [15].

After estimating the under-5 child mortality rate for 52 low-migration countries in this study, we categorized the countries into three groups, as shown in the tables. These groups were formed based on geographical location (African, Asian, and Western countries). In total, data from 52 low-migration countries were analyzed in this study during the period 1990-2015. Table 2 shows the estimated child mortality rate per 100,000 live births for 21 African countries (Angola, Benin, Burkina Faso, Cameroon, Central African Republic, Congo, Ghana, Ivory Coast, Madagascar, Malawi, Mali, Mauritania, Morocco, Mozambique, Niger, Nigeria, Somalia, Sudan, Tanzania, Uganda, and Zambia). It was found that Somalia had the highest child mortality rate (225 per 100,000 live births) in 1990, followed by Malawi (163 per 100,000 live births) and Mali (163 per 100,000 live births), while Mauritania (99 per 100,0000 live births) had the lowest child mortality. Subsequently, in 2015, Somalia also showed the highest child mortality rate (61 per 100,000 live births), while Morocco was estimated to have the lowest (38 per 100,000 live births).

Table 3 shows the estimated child mortality rates for 19 Asian countries. In Table 3, of the Asian countries (Armenia, Bangladesh, Bhutan, China, India, Indonesia, Iran, Japan, Malaysia, Mongolia, Myanmar, Nepal, North Korea, Papua New Guinea, Philippines, Sri Lanka, Thailand, Uzbekistan, and Vietnam), Uzbekistan had the highest child mortality rate (118 per 100,000 live births), followed by Myanmar (116 per 100,000 live births), in 1990, while Japan had the lowest child mortality rate (39 per 100,000 live births). In 2015, Armenia had the highest child mortality rate (45 per 100,000 live births), while Japan had the lowest child mortality rate (12 per 100,000 live births).

Similarly to the process illustrated above, Table 4 presents findings for 12 Western countries (Albania, Argentina, Brazil, Bulgaria, Columbia, Fiji, Honduras, Mexico, Paraguay, Peru, Uruguay, and Venezuela). Of these countries, Albania had the highest child mortality rate (128 per 100,000 live births) in 1990, while Argentina had the lowest estimated child mortality rate (44 per 100,000 live births). In 2015, Fiji had the highest child mortality rate (50 per 100,000 live births), whereas Argentina had the lowest child mortality rate (18 per 100,000 live births).

This study estimated under-5 child mortality rates in 52 low-migration countries by analyzing child population data from 1990 to 2015. A simple method was applied to estimate child mortality. Under-5 mortality is typically understood as the probability of death between birth and the age of 5 years and is usually expressed per 1,000 or 100,000 live births [18]. The results of this study align with those of another study conducted by the World Bank [19], in which the child mortality of Nepal was found to be 33 per 100,000 live births. Similar findings have also been well documented elsewhere in the literature [19,20]. Moreover, most of the African countries had higher rates of under-5 mortality than Asian and Western countries. Nonetheless, under-5 mortality has gradually declined in these 52 countries [21,22]. It may therefore be reasonable assume that all of these countries have made considerable investments in child health policies, advanced medical interventions, and the establishment of rehabilitation facilities and services. Numerous studies have observed similar findings; from 1990 to 2015, the world has remarkably reduced under-5 mortality by two-thirds by following political commitments, combatting poverty and hunger, and implementing favorable policies and interventions regarding the environment, medical technology, and public health [3,4,10,22].

Throughout the world, 15,000 children under the age of 5 died every day in 2017 [4]. African countries are the most directly affected by this issue and account for a high proportion of under-5 child mortality [11], especially in eastern, central, and western Africa. A high burden of communicable disease, lack of strengthened healthcare facilities, poor hygiene and water supplies, severe droughts, and unstable government are possible explanations for child mortality [20,23,24]. Similar findings have been discussed in other studies [20,21], which also mentioned these issues regarding the ongoing burden of child mortality in this region, where significant improvements have yet to be made in child mortality. Therefore, millions of children in these regions face threats to their future due to the constraints of supply and demand regarding services and broader political, social, economic, and environmental determinants [21–24]. In contrast, Algeria, Morocco, and South Africa have achieved progressive reductions in child mortality in the last two decades [25,26]. This improvement may have been due to the breakdown of disparities and gender-discriminatory policies, improved socioeconomic status, good maternal and child health, and an emphasis on sanitation and hygiene programs [27]. Similar findings have been reported in other studies [27,28], which found that Middle Eastern and some southern African countries have made remarkable progress in reducing child mortality since the 1960s [26,27,29]. This progressive decline in mortality is due to the expansion in the literacy rate, increases in living standards, widespread political stability, and control of HIV/AIDS, all of which have led to strong coverage and performance of the healthcare system [29].

Furthermore, of the South Asian countries (Bangladesh, Bhutan, India, Iran, Nepal, and Sri Lanka), India bore the highest burden of child mortality. In Southeast Asia (Indonesia, Myanmar, Malaysia, Philippines, Thailand, and Vietnam), Malaysia showed the highest child mortality rate, and a Western Asian country (Armenia) showed the highest child mortality rate. These persistently high rates of child mortality may be due to infections during birth, birth trauma, low birth weight, early marriage, and low rates of antenatal and postnatal care. Similar findings have been consistently reported in other studies [10,29]. Throughout the world, every day around 19,000 and 16,000 children under the age of 5 years died every day in 2011 and 2015, respectively [4,9]. Half of these deaths occur in South Asian (Afghanistan, India, and Pakistan) and sub-Saharan African countries [9], for reasons including poor health care facilities, conservative societies, war, and conflict [10,30]. In contrast, the under-5 mortality rate is somewhat lower and has been successfully reduced in East and West Asia, followed by Central and South Asia. This may be due to the good coverage of basic services in accordance with fundamental human rights, including antenatal and postnatal care and immunization. Other studies have likewise found the most rapid declines in child mortality in East and West Asia between 1990 and 2015 [14,29]. During this period, low-cost interventions (e.g., oral rehydration service, immunization) and good maternal and child health care facilities have expanded, with appropriate legislation in these countries [14].

Moreover, in Western countries, significant progress has been made in reducing child mortality, with decreases more than three times higher than those in Africa and two times higher than those in Asia. This achievement has been made possible by effective interventions for infectious disease, political commitment, and appropriate investments in medical and nursing facilities and other applicable services, as has also been documented in other studies [22]. Western countries have made progress in expanding access to immunization and other preventive actions for disease control, good sanitation, and hygienic food and water supplies, leading to impressive progress in child mortality [10]. The impact of these economical interventions has proven the effectiveness of universal coverage of fundamental services, which prevented 5.6 million deaths of children under the age of 5 years worldwide in 2016 [10,23]. In this regard, there is a need to continue battling against child morbidity and mortality to achieve the goal of reducing under-5 child mortality by two-thirds between the period of 1990 to 2015, in accordance with the Millennium Development Goals, and to 25 per 100,000 live births in all countries in alignment with the SDGs [10,29]. In this study, we used a simple mathematical method to estimate trends in under-5 child mortality in 52 countries over time based on population data. Children from low- and middle-income countries still have a higher risk of death and are more vulnerable than those in high-income countries. However, the study focused only on 52 countries where there is low migration, and this method is not applicable to high-migration countries.

The study estimated under-5 child mortality rates in 52 low-migration countries using a simple method. The highest child mortality rates were found in Africa, followed by Asia and the West. The findings of this study indicate that more programs should be focused on child health and survival, especially in sub-Saharan Africa and even in some Asian countries.