Timing
Point-in-time data
The point-in-time method has an obvious advantage in
avoiding the risk of recall error, but by definition sampling
is limited to mothers with children under six months of
age. Since so few babies are exactly six months old at the
time of any survey, the 24-hour recall method cannot be
used to estimate how many babies are still exclusively
breastfed at exactly six months of age. Measuring the proportion
of babies who are currently exclusively breastfeeding
between five and six months of age would result in
only a slight overestimate. Some babies 5.0 to 5.9 months
of age may stop exclusive breastfeeding some days or
weeks after the survey. Thus the proportion doing so for a
full six months will be slightly less than what is estimated
by looking at all babies 5.0-5.99 months of age.
A survey of say 3000 children under five years of age
(a common age range covered in, for example, the DHS—
Demographic and Health–surveys), would offer a sample
size of only 50 - 60 infants five to six months of age,
too small to provide an estimate stable enough to examine
annual trends for example. Some national surveys
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do overcome this either by having a much larger sample
size or by oversampling infants and may thus sometimes
arrive at a sample of 5.0-5.99 month infants ten times
this large, allowing the use of a one-month age interval
in arriving at a stable estimate of exclusive breastfeeding
continuing until six months of age. This is perhaps the
only way to reliably use the point-in-time indicator to provide
a reliable estimate of the proportion of infants exclusively
breastfed “at” (still not quite “for”) six months.
More common is still to combine all babies currently
under six months of age (sometimes estimates are based
on all babies under four months of age which of course
will yield an even higher percentage). The average age of
the babies in a 0 - 6 months age group is clearly going to
be about three months of age. Even in low-income countries
where many babies may receive little if anything else
for the first 2 - 4 months of life, after that age, the nearly
universal “traditional” pattern of infant feeding was to
introduce supplements well before 6 months of age. Thus
variations in national durations of exclusive breastfeeding
reported using this WHO indicator are heavily dependent
on the extent of exclusive breastfeeding in the first 2 -
3 months. Nevertheless, the WHO indicator is useful and
allows simple comparison among surveys not conducted
on very large sample sizes; it is the misrepresentation and
misreporting of this easily misunderstood indicator that is
a major problem.
For cost reasons, most national surveys are crosssectional
and thus will conduct a 24-hour recall only once.
Even prospective research often uses repeat 24 hour recalls
instead of asking whether any other food or fluid was
introduced since the last questionnaire was administered.
Some research uses a 7-day diary to obtain detailed data
on the current feeding pattern [18] but clearly this is not
feasible for most surveys.