Title: Analyzing Factors Affecting Age at First Birth among Married Women in Somalia: A
Bayesian Shared Frailty Modeling Approach using SDHS 2020
Version: 2 Date: 13 Feb 2025
Reviewer:  Osafu Augustine Egbon
Reviewer's report:
The study provides a rigorous and insightful analysis of the factors influencing the age at first
birth among married Somali women using Bayesian shared frailty modeling. By comparing
Weibull, log-normal, and log-logistic models, the authors effectively identify  the best model
fit and highlight key determinants of birth timing. This is a highly relevant and important topic,
and the authors have done a good job in presenting a well-structured manuscript with a thorough
analytical approach. However, I suggest that the authors further address the following comments
to enhance the clarity, robustness, and overall impact of the study.
1. The introduction presents statistics but doesn’t clearly highlight the research gap or novelty
of the study. It should explicitly state: What gaps exist in previous research on age at first birth
in Somalia? How will the Bayesian shared frailty model improve understanding compared to
existing methods?
2.  The methodology could be introduced in a more structured manner.  Instead of listing
methods, introduce them in a way that shows their relevance in the introduction for non-technical
readers.
3. In Equation 1, the notation should be consistent. If t is the survival time, it should be f(t)
instead of f(x), as t is used elsewhere.
4.  Eqn 5: The notation should be clarified: the variance term is sometimes written as #2 instead
of \delta^2. If \delta  is used for standard deviation, it should be explicitly stated around the
formula.
5. the integral defining #(z)  in Eqn 6 has formatting issues, making it hard to read.
6. The notation #_0(t)  should be explicitly defined earlier
7.  The notations in eqn 11 and eqn 7 are not consistent
8. In the Result section 3.1 : It is stated that individuals with "No Education (83.17%)" are all
censored, implying that none had a first birth during the study period. However, the discussion
also suggests that individuals with secondary and higher education tend to have longer times to
first birth. If no one with no education has given birth, how can it be inferred that those with
higher education have longer times? This should be clarified.
9.  The Kaplan-Meier estimation states that Somali women have a median survival time of 19
years post-marriage before having their first child. This is highly implausible given the general
reproductive patterns in Somalia, where early childbearing is common. The authors should
double check to ensure that this is correct.
10  The reported frailty variance is 841.933, which is extremely high, indicating significant
unobserved heterogeneity. If frailty effects are this strong, it may suggest that individual-
level variations dominate over modeled covariates, making the model’s explanatory variables
relatively weak. The author should clarify whether this level of variance undermines the overall
power of the selected frailty model.
11. Many covariates in the Bayesian Weibull AFT model have negligible or non-significant
effects, with credible intervals crossing zero. This suggests that key socioeconomic and
demographic factors do not substantially influence the time to first birth, which contradicts
existing literature on fertility determinants. The authors should re-examine for potential model
problems.
12. The author should include an  interpretation of Beta[1] (with a mean of 2.805).
13. In section 4, The discussion jumps between different models (log-logistic, Weibull,
lognormal), different estimation methods (frequentist vs. Bayesian), and different study
populations (Somalia, Ethiopia, Nigeria, Indonesia, Nepal). There should be  justification for
these shifts.