Dear All:

Rachel made some very good points about using tools appropriately by knowing what 
decisions you would make if you had the information.  This is key in a tool's utility and 
can distinguish between when it is a tool or a gadget according to Linda Smith's analogy.

I completely reread the article by the neonatologists on test weighing and found we ALL 
missed something in their article.  They actually said that test weighing was "accurate", 
but not "precise".  There was a huge discussion about the "accuracy" of test weighing on 
Lactnet despite the fact that the neonatologist said it was accurate.  In fact, the 
neonatologists did NOT test precision at all.

I did a little mini study that yielded surprising results to me.  I used a bottle that didn't 
have fine gradations and compared the volumetric assessments with the weight estimates 
of the contents of that bottle.  The PRECISION of both the test weighing AND the 
volumetric assessments of 10 different samples was within a fraction of a g or ml of each 
other.  The maximum of any difference in measurements of the same sample was only 2 
g or 2 ml.  The volumetric assessment was a bit biased because the two measurements 
were taken close enough together that the previous value could be "remembered" and 
may have influenced the second measurement.  

In terms of ACCURACY, I did not define which of the two was "truth".  The mean 
difference between the two methods was only 2 g or 2 ml, with the observation of the 
volume being slightly higher --- particularly in the higher range of the bottle where the 
gradations were spaced farther apart.

I haven't tested this yet with drop in liners --- and I will do a trial to remove "recall" bias.   
And I will also be trying to get at the dribble and wiggle factors.  

But, please ---- no more discussions of the accuracy and precision of these estimates 
with either eyeballing bottles or test weighing.  The important issue is how scales are 
used and how decisions are made!!!!  Not accuracy or precision.

My conclusion is that the neonatologists that did the study on test weighing were VERY 
sloppy indeed.  Most of the error was probably in sloppy techniques, not the instruments. 

Best, Susan Burger

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