On Tue, 02 Sep 2008 12:47:07 -0700, BottleBob
wrote:


Accuracy:
Accuracy refers to the closeness between measurements (observations)
and their expectations ("true" values). The farther a measurement is
from its expected value, the less accurate it is.

Precision:
Precision pertains to the closeness to one another of a set of
repeated observations of a random variable. Thus, if such observations
are closely clustered together, then these observations are considered
to have been obtained with high precision.


An easier visualization:

Accuracy - all in the 10 ring

Precision - a 0.375" group, but it might be anywhere on the target.


RWL

An easier visualization:

Accuracy - all in the 10 ring

Precision - a 0.375" group, but it might be anywhere on the target.


RWL

I don't think you can have the same definition "accuracy" when referring to
weaponry and measurements, though this is a bit of a subtelty -

in weaponry, accuracy refers to hitting (or at least coming close) to the
target - in fact a standard measurement might be CEP (circular error
probability) - in WWII the CEP of a bomb might be measured in hundreds of
yards, in today's precision guided munitions world, we can expect a much
smaller number. This is analagous to the definition above.

But in measurement, there is no target there is just the "real" value of the
thing, and the value you measure.

I also think the spreadsheet example is useful. If you divide 100 by 3, you
get 33.33333333, but you only had single digit (presicion? accuracy?
resolution?) to start with, you cannot gain accuracy by calculation alone.


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