Dear Heather:

Dependability is one component of Precision:

Precision is comprised of:
REPEATABILITY: the variation arising when all efforts are made to keep the conditions constant by using the same estimation process AND
1) the same observers (operators) AND
2) the same instruments (measurement devices), AND by 
3) repeating the estimates OVER A SHORT INTERVAL.

REPRODUCIBILITY: the variation arising when the estimation process is kept constant while varying specific conditions such as
1) different observers = inter-observer variation OR 
2) different instruments = inter-instrument variation), OR 
3) by the repeating the estimates OVER A LONG DURATION = dependability.

To give an example that isn't related to test weighing:
If you measured prolactin levels right after a lactating mother fed her baby and measured them an hour later -- you would get different results.  It MATTERS when you take the levels of prolactin.  This is one extreme example of when dependability is critical in how you interpret an indicator.

The authors of the study actually thought they were testing DEPENDABILITY, which is a component of REPRODUCIBILITY.  Because evaporative water loss occurs over time, it is not something that happens when you immediately repeat a measurement.  By their own experiment they showed not only that there was NO evaporative water loss of any statiscal or biological significance.  Therefore, 15 minutes was too short a time interval over which to test the dependability and what you are really left with is a test of:

1) the same observers (operators) AND
2) the same instruments (measurement devices), AND by 
3) repeating the estimates OVER A SHORT INTERVAL.

which is PRECISION.

Best, Susan

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