National and regional under-5 mortality rate by economic status for low-income and middle-income countries: a systematic assessment

Abstract

Background: The progress to achieve the fourth Millennium Development Goal in reducing mortality rate in children younger than 5 years since 1990 has been remarkable. However, work remains to be done in the Sustainable Development Goal era. Estimates of under-5 mortality rates at the national level can hide disparities within countries. We assessed disparities in under-5 mortality rates by household economic status in low-income and middle-income countries (LMICs).

Method: We estimated country-year-specific under-5 mortality rates by wealth quintile on the basis of household wealth indices for 137 LMICs from 1990 to 2016, using a Bayesian statistical model. We estimated the association between quintile-specific and national-level under-5 mortality rates. We assessed the levels and trends of absolute and relative disparity in under-5 mortality rate between the poorest and richest quintiles, and among all quintiles.

Findings: In 2016, for all LMICs (excluding China), the aggregated under-5 mortality rate was 64·6 (90% uncertainty interval [UI] 61·1-70·1) deaths per 1000 livebirths in the poorest households (first quintile), 31·3 (29·5-34·2) deaths per 1000 livebirths in the richest households (fifth quintile), and in between those outcomes for the middle quintiles. Between 1990 and 2016, the largest absolute decline in under-5 mortality rate occurred in the two poorest quintiles: 77·6 (90% UI 71·2-82·6) deaths per 1000 livebirths in the poorest quintile and 77·9 (72·0-82·2) deaths per 1000 livebirths in the second poorest quintile. The difference in under-5 mortality rate between the poorest and richest quintiles decreased significantly by 38·8 (90% UI 32·9-43·8) deaths per 1000 livebirths between 1990 and 2016. The poorest to richest under-5 mortality rate ratio, however, remained similar (2·03 [90% UI 1·94-2·11] in 1990, 1·99 [1·91-2·08] in 2000, and 2·06 [1·92-2·20] in 2016). During 1990-2016, around half of the total under-5 deaths occurred in the poorest two quintiles (48·5% in 1990 and 2000, 49·5% in 2016) and less than a third were in the richest two quintiles (30·4% in 1990, 30·5% in 2000, 29·9% in 2016). For all regions, differences in the under-5 mortality rate between the first and fifth quintiles decreased significantly, ranging from 20·6 (90% UI 15·9-25·1) deaths per 1000 livebirths in eastern Europe and central Asia to 59·5 (48·5-70·4) deaths per 1000 livebirths in south Asia. In 2016, the ratios of under-5 mortality rate in the first quintile to under-5 mortality rate in the fifth quintile were significantly above 2·00 in two regions, with 2·49 (90% UI 2·15-2·87) in east Asia and Pacific (excluding China) and 2·41 (2·05-2·80) in south Asia. Eastern and southern Africa had the smallest ratio in 2016 at 1·62 (90% UI 1·48-1·76). Our model suggested that the expected ratio of under-5 mortality rate in the first quintile to under-5 mortality rate in the fifth quintile increases as national-level under-5 mortality rate decreases.

Interpretation: For all LMICs (excluding China) combined, the absolute disparities in under-5 mortality rate between the poorest and richest households have narrowed significantly since 1990, whereas the relative differences have remained stable. To further narrow the rich-and-poor gap in under-5 mortality rate on the relative scale, targeted interventions that focus on the poorest populations are needed.

Funding: National University of Singapore, UN Children's Fund, United States Agency for International Development, and the Bill & Melinda Gates Foundation.

Figure 1

Data availability Countries are coloured by regions. Circle size is proportional to the number of datapoints available for each country. This map does not reflect a position by the UN Inter-agency Group for Child Mortality Estimation agencies or those of the institutions to which the authors are affiliated on the legal status of any country or territory. The dotted line represents approximately the Line of Control in Jammu and Kashmir agreed upon by India and Pakistan. The final status of Jammu and Kashmir has not yet been agreed upon by the parties. The final boundary between Sudan and South Sudan has not yet been determined. The final status of the Abyei area has not yet been determined. The borders are not up to the UN standard

Figure 2

Quintile-specific under-5 mortality rate from 1990 to 2016, for all low-income and middle-income countries (excluding China) combined (A) Under-5 mortality rate and (B) percentage of under-5 deaths by year. Curves are point estimates. Shaded areas are 90% uncertainty intervals. The first quintile is the 20% poorest quintile and the fifth quintile is the 20% richest.

Figure 3

Under-5 mortality rate in 1990 and 2016, for all low-income and middle-income countries (excluding China) combined and by region (A) Point estimates for under-5 mortality rate in each quintile in 1990 and 2016. Coloured dots show the point estimates for under-5 mortality rate in each quintile. The first quintile is the 20% poorest quintile and the fifth quintile is the 20% richest. The distance between the first and fifth quintiles represents the difference in first and fifth quintile mortality rate. Regions are in descending order of point estimates for under-5 mortality rate in the first quintile in 2016. (B) Ratio of first to fifth quintile mortality rate. Dots are point estimates. Error bars denote 90% uncertainty intervals. (C) Absolute decline and (D) percentage decline in under-5 mortality rate in the first (poorest) and fifth (richest) quintiles in 1990–2016. Error bars represent 90% uncertainty intervals. Regions are in descending order of point estimates in the first quintile. (E) Poorest (first) quintile under-5 mortality rate and (F) richest (fifth) quintile under-5 mortality rate. Curves are point estimates. Shaded areas are 90% uncertainty intervals.

Figure 4

Overview of the average association between the ratio of under-5 mortality rate in the first to fifth quintiles and national-level under-5 mortality rate Observed ratios of first to fifth quintile mortality rate are plotted against decreasing national-level under-5 mortality rate (grey dots) and the model results of the average association between ratios of first to fifth quintile mortality rate and national-level under-5 mortality rate are in red. Curve is point estimates. Shaded area is 90% uncertainty intervals.

Figure 5

Ratio of first to fifth quintile mortality rate against difference in first and fifth quintile mortality rate in 99 low-income and middle-income countries with empirical data by national-level under-5 mortality rate in 2016 The size of the circle is proportional to the national-level of under-5 mortality rate (UN Inter-agency Group for Child Mortality Estimation 2017 estimates) in 2016. Circles are colour-coded according to the region each country belongs to. Country codes are International Organization for Standardization country codes. The box in dashed lines in the bottom left corner contains countries with a difference of less than 15 deaths per 1000 livebirths and a ratio of less than 1·5, and the box in the top right corner contains countries with a difference of more than 30 deaths per 1000 livebirths and a ratio of more than 2·5. AFG=Afghanistan. AGO=Angola. ALB=Albania. ARM=Armenia. AZE=Azerbaijan. BDI=Burundi. BEN=Benin. BFA=Burkina Faso. BGD=Bangladesh. BLR=Belarus. BLZ=Belize. BOL=Bolivia. BRA=Brazil. BTN=Bhutan. CAF=Central African Republic. CIV=Côte d'Ivoire. CMR=Cameron. COD=Democratic Republic of the Congo. COG=Congo. COL=Colombia. COM=Comoros. DOM=Dominican Republic. DZA=Algeria. EGY=Egypt. Eritrea=ERI. ETH=Ethiopia. GAB=Gabon. GEO=Georgia. GHA=Ghana. GIN=Guinea. GMB=Gambia. GNB=Guinea-Bissau. GNQ=Equitorial Guinea. GTM=Guatemala. GUY=Guyana. HND=Honduras. HTI=Haiti. IDN=Indonesia. IND=India. IRQ=Iraq. JOR=Jordan. KAZ=Kazakhstan. KEN=Kenya. KGZ=Kyrgyzstan. KHM=Cambodia. LAO=Laos. LBR=Liberia. LSO=Lesotho. MAR=Morocco. MDA=Moldova. MDG=Madagascar. MDV=Maldives. MKD=Macedonia. MLI=Mali. MMR=Myanmar. MNG=Mongolia. MOZ=Mozambique. MRT=Mauritania. MWI=Malawi. NAM=Namibia. NER=Niger. NGA=Nigeria. NIC=Nicaragua. NPL=Nepal. PAK=Pakistan. PER=Peru. PHL=Philippines. PRY=Paraguay. PSE=Palestine. RWA=Rwanda. SDN=Sudan. SEN=Senegal. SLE=Sierra Leone. SLV=El Salvador. SOM=Somalia. SRB=Serbia. SSD=South Sudan. STP=São Tomé and Príncipe. SUR=Suriname. SWZ=Swaziland. SYR=Syria. TCD=Chad. TGO=Togo. THA=Thailand. TJK=Tajikistan. TKM=Turkmenistan. TLS=Timor-Leste. TUN=Tunisia. TUR=Turkey. TZA=Tanzania. UGA=Uganda. UKR=Ukraine. UZB=Uzbekistan. VNM=Vietnam. VUT=Vanuatu. YEM=Yemen. ZAF=South Africa. ZMB=Zambia. ZWE=Zimbabwe.