Accuracy, precision, and I want my billion dollars

Subject: Accuracy, precision, and I want my billion dollars
From: "John Hollinrake" <john_h -at- telusplanet -dot- net>
To: "TECHWR-L" <techwr-l -at- lists -dot- raycomm -dot- com>
Date: Sun, 3 Dec 2000 04:30:57 -0700

I'm beginning to wonder how many people really understand the correct usage
of accuracy, precision, and efficiency. I keep seeing them misused on this
list, and I think it is important that people writing technical
documentation understand these terms.

The difference between accuracy and precision can be explained using a dart
board analogy.

If you keep hitting bulls eyes, then your throws are both accurate and
precise.

If you consistently hit 2 inches from the centre ring in every direction,
then you are throwing accurately (on average, you are throwing bulls), but
imprecisely.

If you are always hitting double 19, when you're aiming for a bull, then you
are throwing precisely, but inaccurately.

And of course, if your throws land in random spots on or off the board, your
throws are both inaccurate and imprecise.

If you have been using these terms incorrectly, don't worry: you are not
alone. I first learned the clear distinction in their use from a professor
of experimental design, who was also the editor of the Canadian Journal of
Chemical Engineering. He told us that more than half the authors submitting
to that journal also used the terms accuracy and precision incorrectly.

As for my billion dollars, on Saturday Andrew Plato said:

"Find me a writer (any human) who works with mathematical precision and I
will
gleefully give you a billion dollars."

Precision is a relative term, and as pointed out above, has nothing at all
to do with whether the writer is close to achieving anything. Once you
measure precision (typically with some kind of standard deviation or
variance from a mean), then it has become mathematical. So we are all
working with mathematical precision. The valuation of that precision varies
from writer to writer. So pay up buddy :). Naw I'll let you off -- if you
had a billion dollars I doubt you'd be reading this crap.

Cheers,

John





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