Page 74 - IJPS-7-2

International Journal of
Population Studies Age-adjusted measures for fertility transition

conditional contribution is positive. This means that in the abovementioned example, will treat births from
the characteristics and the coefficients were positively 15 years ago to produce a distinct measure of fertility rate
associated with the decrease in marital fertility. The results separate from the measure based on a time period after
reported in Figure 5 that highlights how the use of CEB and the introduction education, health, and family planning
ASMFR as dependent variables affects the results. In the infrastructures. This is the reason why ASMFRs were more
period 1988 – 1994, the results based on ASMFR suggest effective at reflecting the marital fertility transition and
that the changes in characteristics of the sample by age stalls presented in the results section.
group and education did not positively support the rapid The results from the illustrative multivariable
decrease in marital fertility rates of Zimbabwe. This was decomposition analysis showed that the conditional
in complete contrast with the results based on the analysis percentage contributions based on the analysis of ASMFRs
of CEB which suggested that compositional characteristics were intuitive, while those from the analysis of CEB were
had a notable positive impact on the decrease of marital sometimes counterintuitive. The reason for this is linked
fertility. Because characteristics measure the distribution of
the sample, a look at the changes in the sample distribution to an extent with the 15-year illustration in the preceding
paragraph. In this study, we used education as one of the
reveal that the results based on ASMFR are more realistic predictor variables. Suppose a cohort of women with only
compared to those from CEB.
primary schooling completed had an average CEB of three
th
4. Discussion births before their 20 birthday during a period when
there was no access to education and health services. This
This study found that the CEB and ASMFRs (TMFRs) have cohort then goes on to have access to secondary education
fundamental implications on the nature of findings from and health services from their 20 birthday such that by
th
the investigation of drivers of marital fertility transition. age 25 their average CEB remains at three, but they have
The main finding of this study was that, compared to the completed secondary schooling. In this case, there is no
cumulative CEB, ASMFRs represent an arguably more change in the outcome variable, but the independent
effective outcome measure in the multivariable analysis of variable education status has changed significantly.
the determinants of marital fertility transition. Compared Analyzing this relationship between CEB and education
to the ASMFR, the CEB tended to underestimate the using the OB decomposition will produce large and
magnitude of marital fertility decline and stall and this counter intuitive conditional percentage contributions of
impacts on the relative importance of the determinants education status. This is because the predictor variable, has
of fertility change. The superior effectiveness of ASMFRs improved but the dependent variable remains unchanged,
emanates from the reference time period it is derived giving the impression that education did not have any
from, which is considered current. Consequently, the effect on fertility. Substituting CEB with ASMFRs in this
ASMFRs capture the period changes in the age patterns of case, the latter will be able to decrease in the births due
fertility. The period changes are also associated with the to the increase in education status and the change in the
changing socioeconomic characteristics of the women reproductive behavior associated with the shift from
and their wider communities of residence. For instance, in primary to secondary education. Consequently, the OB
communities lacking education and health infrastructure, decomposition will produce percentage contributions
many women may have more unwanted births thus inflating which are not counterintuitive. This is because the
the average number of CEB as well as period fertility rates. changes in the education status and ASMFRs will have
If over a 15-year period, there is high investment in social commensurate period references unlike the case with CEB,
infrastructure and many women start having access to where both primary and secondary education attainment
schooling, adult education, and family planning programs will be associated with three births.
and health services, the impact will be a reduction of
unwanted births which reduce the levels of period fertility. The importance of using age-adjusted measures is
When analyzing the fertility change using CEB, births apparent when critically reflecting on the findings of the
which occurred before education, health infrastructure, present study in relation to those from existing literature.
and family planning services were introduced are also In this study, the coefficients which measure behavior
counted in the outcome measure such that unwanted births change effects on fertility were shown to be more closely
from 15 years ago will continue to influence the estimate of associated with the trends in marital fertility rates. This
the level of fertility in the current period. This nature of contrasts somewhat with the studies by Ariho, et al. (2018)
CEB is the underlying reason why the CEB was found to and Ariho & Nzabona (2019) which reported that changes
underestimate the change in marital fertility levels between in characteristics drove the decline in the mean number of
successive DHS surveys. The ASMFRs, contrary to CEB CEB in Uganda between 2006 and 2011, thus concluding

Volume 7 Issue 2 (2021) 68 https://doi.org/10.36922/ijps.v7i2.354