If one steps back from the acronyms, analogies to crops and humans, and 
other mathematical games it is not really that complicated.  A lot 
depends on your confidence with the time frame from a mite "count", 
when it reflects in damage, and when a treatment may be needed.  If you 
take mathematical projections to the extreme, even one mite in a colony 
is trouble, eventually.  If you are not aware of the natural cycles of 
infestation and where economic injury does happen many mites will give 
you trouble, immediately.

So the practical and realistic, and responsible, "IPM"-(pick whatever 
acronym or buzzword you want)-based approach is to work with the 
knowledge of the pest, make as informed decisions as possible, and 
treat accordingly.  The fact that we deal with variability, and work 
with incomplete information, does not negate the value of the effort.  
There is no reason these concepts cannot be applied by the hobbyist or 
small sideliner.  If anything, they have more time per colony, and many 
can afford to play a bit with the risks involved.  I would bet most 
losses of colonies occur at the higher end of the economic damage scale 
and come from ignorance or wishful thinking.  Had varroa mite "counts" 
been taken at critical times, the damage and losses would have been 
mostly predictable- within the limitations of biological variability, 
shared by crops, humans, and bees. 

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