In our study using the Stratified Cox PH model, the multiple or twin birth type children had more than 5 times higher risk of death compared with single birth type children. Many studies showed that birth type of child was a significant determinant factor (8–10). But, other study from Nigeria had reported the reverse of this result. The odd of having infant/child mortality was 1.87 times greater for children with single births as opposed to those with multiple births (11).
In the study, children from family sizes of 4 to 6 members and above 6 members had 0.77 and 0.69 times low risk of dying before the age of five as compared to children from family sizes of 1 to 3 members, respectively. This is consistent with a study by (8). But contradict with the study by Gebretsadik carried out in Ethiopia found an inverse relationship between under-five mortality and family size in 2011 Ethiopia demography and health Survey data (10).
Children from rich wealth index households had 0.68 times lower risk of dying before the age of five as compared to poor wealth index households. They had decreased the death rate by 32%.This was consistent with the findings by some previous studies. These households have better housing conditions, better nutrition, and hence they may be able to afford better medical attention and care thus significantly enhancing the survival probability of all their children (Bello and Joseph, 2014; O et al., 2016; Yu et al., 2018).
In our study, children were delivered in private health sector had 1.6 times high likely of dying before celebrating their 5th year of birth than children were delivered in public health sector. They had increased the death rate by 60%.But, there was no statistically significant difference between children were born in home with compared children were born in public health sector. This finding inconsistent with prior studies by (14–16).
In the study, children from parents were listening radio for at least once a week had 0.7 times less likely to die than children from parents were not listening radio. They had decreased the death rate by 30%.This study explicitly shows the existence of inconsistency in the distribution of under-five mortalities with a study (17).
Our study suggests that mortality rate was higher in rural area. This is on the ground that those living in the urban area have access to improved water supply, improve sanitation facilities, unlimited access to healthcare as well as other social and economic services. Thus, the likelihood of under-five mortality was 1.5 times high among children residing in rural areas as compared with their urban counterpart. This concurs with previous studies in and outside Ethiopia (4, 10, 16, 18).
Our findings showed that the under-five children from Afar, Somali and Harari geopolitical regions of Ethiopia were significantly associated with the highest likelihood of under-five death as compared with children from Addis Ababa city. This high risk might be attributed to social improvement in the community, population density, territorial advancement, as well as regional economic resources (5, 19–21).
In our study using the multilevel mixed-effects using the lognormal parametric model, in the fixed-effect model the covariates like child’s sex, number of children aged 5 and U5, type of birth, size of child at birth, months of breastfeeding, family size, wealth index, place of delivery, place of residence, and frequency of listening radio were the risk factors for the mean survival times of under-five children at 5% level of significance. Other similar findings also found that factors such as child’s sex, type of birth, total number of children, breastfeeding, size of child at birth, family size, wealth index, place of delivery, type of residence, and frequency of listening radio were found as a significant factors (3, 16, 17, 21, 22).
In our study, the mean survival time of female children is exp (1.8) = 6.05 times longer than male children with 95% CI is between 2.5 and 13.3. A similar study using the analysis of 28 Demographic and Health Surveys in Sub-Saharan Africa countries, and other study from Uganda showed that female children had reduced risks of dying before 5 years of age compared to male children (16, 23).
The mean survival time for multiple birth type of the children was exp (-9.9) = 0.034 times less than single birth type of children with 95% CI was between 0.02 and 0.06. This result was consistent with the studies (5, 24).
In the multilevel lognormal parametric model, the two estimated variances of the random-intercept effects in the mean survival times of under-five children between regions and households are 1.7 and 0.9, respectively. These indicated that we have enough evidence for the existence of unobserved heterogeneities between regions and households. And, there was high variation between regions as compared between households. Thus this study provided that there were unmeasured factors other than these included in our analysis that were caused the clustering of under-five children mortality in some households and regions.
This random-intercept effect between region level was supported by other similar studies using gamma frailty model which found that the variance of the frailty term (Regional frailty) θ = 0.145 with p-value < 0.05 (3) used 2016 EDHS data, and study using multilevel logistic regression model showed that the regional level variance of the under-five children mortality was 0.218 (5) used 2011 EDHS data. And, a study from Nigeria using multilevel Cox proportional hazard regression model also founded that there were regional variations in under-five children mortality based on considering community-level variables (11, 16, 21).