Breast milk is known to be very essential for the baby. It has the perfect
blend of nutrients in the exact right amounts for baby`s nutritional needs.
Breastfeeding is also an important contributory factor for healthy mothers.
Breastfeeding promotes health, helps to prevent infant diseases and reduce
health care costs (Hausman, 2003; Pediatrics, 2005).
The World Health Organization (WHO) and the United Nations Childrens
Fund (UNICEF), as well as many other health care organizations, currently
suggest that babies should be exclusively breastfeed for the first six
months of life and thereafter to continue breastfeeding for two years
and beyond. Complementary foods should be introduced when the baby is
six months old (WHO, 2003; Unicef, 2004). The teaching of Islam has acknowledge
and emphasized this fact earlier, where in the Al-Qur`an is written that
breastfeeding is a must for all mothers who can do and weaning should
be carried out at about the time when the baby is two years of age.
Since 1970, the Ministry Health of Malaysia has implemented several strategies
and conducted many activities to promote breastfeeding. The Malaysian
National Breastfeeding Policy states that all mothers are encouraged to
breastfeed their baby completely for between four to six months and continue
to breastfeed until the child is two years old. In 1993, the program called
Baby-Friendly Hospital Initiative (BFHI) was launched for the first time
in Malaysia. The Hospital Rakan Bayi in Malaysia, which is an example
of a program identified under the BFHI, involves campaign to create conducive
conditions in the hospital particularly for mothers who wish to breastfeed
their babies successfully (susuibu.com, 2004; Health, 2006).
In this study, with using the data of Malaysian Family Life Survey reported
by National Population and Family Development Board (1994), we investigate
which factors are significantly related to the breastfeeding duration
using the quantile regression approach. The factors include are place
of living, ethnic group, religion, mother`s education, mother`s employment,
child`s gender, mother`s age and total number of children in the family.
Both commercial formula milk and breast milk are the main source of nutrition
for the baby. Although formula milk has more protein, breast milk is still
the best for baby. Breast milk has all the essentials required by the
baby, such as water, protein, carbohydrates, fats, vitamins and minerals,
all of which are available in correct proportions. Considering the beneficial
effect of breastfeeding on the survival of the baby, World Health Organization
recommended that all mothers do breastfeed their babies for a sufficient
length of duration.
Many studies have been carried out to determine factors which influence
the duration of breastfeeding. Using data for Sri Lanka, Akin et al.
(1981) has shown that mother`s age, mother`s work, usage of pill and number
of children in the family as factors that can influence the duration of
breastfeeding. Blyth et al. (2004) has also shown that maternal
age in Australian population is related to breastfeeding. Jacknowitz (2004)
found out that mother`s age, education of mother, ethnic and birth place
are factors which have significant effect on influencing breastfeeding
pattern. Factors influencing the success of breastfeeding are very complex,
involving psychological and physical interaction between the baby and
mother and difficulties for this interaction can lead to discontinuation
(Jelliffe and Jelliffe, 1978; Jacknowitz, 2004; Nutriweb, 2005).
Breastfeeding duration is one of the factors that has been shown in many
studies to have a strong association with the healthy growth and development
of infants. Breastfeeding also protects babies against the risk of allergy
and contribute to child spacing for the mothers (Pediatrics, 2005). The
maternal bond is strengthened through breastfeeding, with the hormonal
releases giving the mother positive feelings of nurture towards the child.
Recent study (Uauy and Peirano, 1999) shown that children who have been
breastfed are found to obtain the average score on the IQ tests higher
than those who have not been breastfed. Studies that have been carried
out by WHO have shown that malnutrition could cause 60% of the 10.9 million
deaths annually among children under five. These deaths could possibly
be associated to the feeding practices, particularly during the first
year of babies` life (WHO, 2003).
MATERIALS AND METHODS
The breastfeeding data used in this study are based on retrospective
study, reported in the Malaysian Family Life Survey (MFLS). Based on the
MFLS report, 1,591 respondents were selected for the analysis considering
that they have satisfied the requirements for this study. The identified
respondents, represented 4,444 sample of households in Peninsular Malaysia,
where each household consist of an ever married woman under the age of
50 years, with at least one child under the age of seven. This survey
focused on the breastfeeding experience of the mothers to their youngest
child, even if only for a short time and up to 29 months.
Based on the data gathered regarding the respondents, a summary for the
characteristics of mothers are as shown in Table 1.
Based on the analysis of lengths of breastfeeding duration, it is found
that most mothers practiced breastfeeding during the first two months
of their babies` life. The distribution of breastfeeding duration is skewed,
as shown in Fig. 1.
Quantile regression: As described by Gilchrist (2000), quantile
is defined as the value that corresponds to a specified proportion of
a sample or population. Thus, we may defined τth quantile as the
value which divide the data into two parts, the τ fraction of the
data below it and 1-τ fraction of the data above it and 0<τ<1.
Median is a commonly used quantile, which is equal to 0.5th quantiles
of the ordered data. Quantiles regression as introduced by Koenker and
Bassett (1978), is a statistical method used to estimate models based
on conditional quantile functions.
||Number of respondents according to different variables
|| Distribution of breastfeeding duration
Unlike the classical linear regression methods that are based on minimizing
sums of squared residuals and to estimate only one model based on conditional
mean functions, quantile regression methods are based on minimizing absolute
residuals and intended to estimate conditional median functions and a
full range of other conditional quantile functions (Koenker and Hallock,
2001). When compared to classical regression approach, quantile regression
is more comprehensive since it provides the conditional distribution of
variable of interest, say Y given a certain value of an explanatory variable
X, at various quantile positions.
Consider a classical linear regression model;
||1xp row vector of constants so that E(yi) = xiβ
||px1 vector of parameters
The regression estimator can be estimated by minimizing the sum of squared
= Predicted value for the ith observation.
When estimating the conditional median, we can define the solution as
a problem of minimization the sum of absolute residuals, which can be
We define a linear model for the ith quantile as:
Analogous to the concept of median, Koenker and Basset (1978) proposed
a complete and different method for estimation of an unknown value, say
α, for any τ in the interval (0,1), which may be defined as
any solution to the minimization problem of the equation:
In estimating models for conditional quantile function, we minimize a
sum of asymmetrically weighted absolute residuals. This will contribute
to different weights to positive and negative residuals. The general τth
sample quantile, which is the analogue to Eq. 5 can be
and equivalently written as:
Several software packages can be used to implement the quantile regression
method, such as S-plus (Yu, 2003), R-program (Faraway, 2005; Verzani,
2005) and Stata. In this research, R software was used to model the relationship
of the duration of breastfeeding with characteristics of mothers as using
the quantile regression approach.
RESULTS AND DISCUSSION
In this study, quantile regression approach is used to examine the relationships
between the duration of breastfeeding and some potential explanatory variables.
According to the different τth quantile, it is found that
the distribution of breastfeeding duration as provided by respondents,
is shown in Table 2.
It is interesting to notice that about 35% of the respondents practiced
breastfeeding during the first month period of their babies life. Fifty
percent of the respondents, weaned breastfeeding when their baby are less
than two months old, as shown by the mean duration of two months for the
0.5th quantile. About 10% of mothers have breastfed their babies for the
period of 19 months and more.
To examine the relationship between the duration of breastfeeding and
some potential explanatory variables, the quantile regression approach
is used for the analysis. In most of the analysis of breastfeeding duration,
least square regression method has been employed. However, a more complete
picture of the covariate effects can be provided based on the conditional
quantiles regression functions. The variables are found to be significant
in relation to the breastfeeding duration are place of living, religion
and total number of children in the family. The reference categories that
are used to define the place of living, religion and total number of children
are metropolitan, Islam and one or two children in the family, respectively.
The pattern of the relationships between these variables with the duration
of breastfeeding for various conditional quantiles function, are as given
in Fig. 2.
||Distribution of breastfeeding duration according to
the different τ quantile
||Quantile regression estimation: breastfeeding duration
The dashed lines in Fig. 2 shows the ordinary least
squares estimate of the conditional mean effect, with two dotted lines
represent to 90 percent confidence intervals of mean. Duration of breastfeeding
practiced by mothers who live in urban area is almost constant over the
whole range of the distribution, except for the 0.8 and 0.85th quantiles.
Mothers who live in rural area breastfed their babies for a longer period
compared with mothers in the metropolitan. Using metropolitan as the reference
category, the difference between breastfeeding durations for rural and
metropolitan can be observed based on the mean at 0.4 and 0.6th quantiles,
as indicated by the longer breastfeeding period of half and one month,
respectively. The longest breastfeeding period can be seen at 0.8th quantile,
employing that on the average mothers living in the rural practiced breastfeeding
six months longer than mothers in the metropolitan.
|| Quantile regression estimation: breastfeeding duration
|***: p-value≤0.001; **: p-value≤0.01; *: p-value≤0.05
Considering the religion, it is found that the mothers who believe in Christian,
Hindu and Buddhist breastfed their babies for a shorter period, compared to
mothers who believe in Islam. These patterns seemed to be consistent through
out the whole range of the breastfeeding duration.
Children who live in the family with 3 or 4 children and more than 4
children, experienced breastfeeding duration longer than children who
live in the family which have 1 or 2 children. The longest period of breastfeeding
is found in the family whose have more than 4 children. This result suggested
that the breastfeeding period practiced by mothers who have 3 or 4 children,
are longer half month as shown by the mean for the 0.4 to 0.5th quantiles
and longer by one month as shown by the mean for the 0.6 to 0.8th quantiles.
Based on the means of corresponding to 0.4, 0.5, 0.6 and 0.8th quantiles,
mothers who have more than 4 children are found to breastfeed their babies
by longer period 1.0, 1.5, 2.0 and 4 months, respectively, compared with
mothers who have 1 or 2 children.
Furthermore, Fig. 2 show that some quantile regression
estimates lie outside of the confidence intervals based on the ordinary
least squares regression, indicate which the effects of these covariates
on the mean breastfeeding duration are not constant, depending on the
value of the independent variable. A summary to describe the explanatory
variables which are found to be significantly related to breastfeeding
duration for certain quantile position, is shown in Table
The method of quantile regression can give a clear picture on the relationship
between the explanatory variables with the breastfeeding duration for
the whole range of the data distribution considered. Although the variables
that are significant in overall of the model, may vary according to the
quantile position. It is clear that the determinant of breastfeeding duration
in Peninsular Malaysia are place of living, religion and total number
of children in the family, which can be particularly observed for the
higher quantile position.