Fio, your test weight results cause me to comment on something I have
wondered about for awhile, and that is what the accuracy and precision is of
the scales being used to test weigh babies.  Please indulge my chemistry
lesson for a moment:

Accuracy -- how close to the accepted or true value a measurement is, or the
degree of conformity of a measured or calculated value to its actual or
specified value.

Precision -- measures how far from the mean or average of replicate
measurements a particular measurement lies, usually reported as a standard
deviation or average replicate error.  Precision is a measurement of how
closely the analytical results can be duplicated.  With respect to a single
device, put into operation repeatedly without adjustments, "precision"
refers to the ability to produce the same value or result, given the same
input conditions and operating in the same environment.

Step on a scale five times in a row and you will often get five different
weights.  Depending on how far apart these results are from each other and
from the mean, the scale may or may not be very accurate and/or precise.
How precise and accurate are the baby scales in common use in hospitals and
at home?

Your daughter's "loss" of 3 oz. (about 90 ml) after two nursings does
confirm my suspicions about many of these scales.

If indeed they are not sensitive enough to accurately show the difference
between a pre-feed baby and that same baby post-feed, then we are doing
women a disservice in using them.  The scales in the hospital units I have
worked in, although admittedly expensive, were never really questioned in
this regard, and we certainly were never told what sort of standard
deviation one might expect from them.

The digital aspect of the newer scales can also be misleading -- people
assume that since they are capable of reporting a weight to within 5 grams
(or even a gram), that they must be both accurate and precise within plus or
minus 5 grams, but I don't believe this is necessarily so.

Of course, a scale which may not be suitable for pre- and post-feed weights
may be perfectly appropriate for weekly weights, for example.  It is only
when we are trying to measure very small differences that they may not be
reliable.

Also, how often are these scales properly re-calibrated?

Does anyone have any better technical info on this?

Thanks for raising this interesting question, Fio.

Barb Strange

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