K. Jean Cotterman <[log in to unmask]> wrote:
> <Of the 70,148 singleton infants, 65 infants required surgery for PS, 29
> of whom were bottle-fed before PS diagnosis.>
>
> I just don't get it, no doubt due to my inability to make sense of the
> rest of the statistics.
>
> Of the 65 said to require surgery for PS, if you subtract the 29 bottle
> fed babies seems to = 36 of them then who were apparently breastfed to the
> satisfactoy definition of the researchers, who still, nevertheless,
> required PS surgery.
>
> Considering the large group of children they began with, I can't see how
> then that this adds up to the conclusion then that bottle feeding seems to
> be statistically a more remarkable contributor to pyloric stenosis?? Or
> breastfeeding so much less of a contributor?
OK, so around 45% of the PS cases were bottlefed before PS diagnosis.
Statistics 101: You can't even begin to interpret that number without
also knowing the rates of "breastfeeding" and "bottlefeeding" in the
population studied (however these terms were defined during data
collection - both are ambiguous![1]).
To take an extreme but illustrative hypothetical example: if only 2% of
infants were bottlefed at the time of diagnosis, for bottlefed infants
to represent 45% of the infants with PS would demonstrate that
bottlefeeding was associated with a vastly increased risk of PS. If 45%
of infants in the study population were bottlefed and 45% of the PS
cases were bottlefed infants, you'd have no evidence of any influence of
feeding method on PS risk. If 99% of the population were bottlefed and
only 45% of the PS cases were bottlefed, you'd be tempted to conclude
that bottlefeeding might be substantially protective. And so on.
Since this was Denmark (with near 100% initiation rates) and the median
age of diagnosis of PS in the study was a fairly typical 35 days of age,
it won't surprise anyone to note that a large majority of infants were
being breastfed around that age. Therefore 45% of PS cases being
bottlefed at time of diagnosis is a rather massive over-representation.
The rest of the data on that is in the full study, including a graph on
the cumulative risk of PS by age. The study goes on: "It was estimated
that among bottle-fed infants, 0.31% developed PS during the first 4
months after birth compared with 0.05% among infants who were not
bottle-fed during the first 4 months".
The authors consider two possible explanations for their results: that
breastfeeding confers specific protection against PS (osmolarity,
hormones like VIP, protection from hypothetical infectious triggers) or
that bottlefeeding confers specific risk, via either formula factors
(protein, etc) or by actual feeding method (rapidity of intake, larger
milk volumes in the stomach).
One possible explanation that they don't consider to my total
satisfaction (I can be a bit picky) is the possibility that infants who
would go on to present with full-blown pyloric stenosis may have had
early feeding issues that resulted in a higher incidence of
bottlefeeding in the neonatal period.
Lara Hopkins
[1] I poked into the full study for this: they clarify "Only 48 women
(no PS cases) in our study gave their own (45 women) or another mother's
milk (3 women) by bottle. We therefore assumed that the bottle-fed
infants were fed artificial formula milk."
They don't, however, say anything about cup-feeding, tube-feeding,
SNS-feeding, or any other method.
It's also worth noting the missing data - there were actually 80 PS
cases, but 20 were missing feeding data from the 6-month interview and
were therefore excluded.
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