How does accuracy differ from precision in a scientific measurement?

Question

How does accuracy differ from precision in a scientific measurement?

Answer 1

Think of three archers.

One shoots his arrows, and they all end up in, say the third outer target ring, all about 6 inches from the centre, and spaced evenly around.  If you averaged the distances from the centre, the average would be close to the centre, but he never shot an arrow near the centre.  This archer would be said to have a high degree of accuracy, but low precision.

A second archer has much higher skill; but has forgotten a factor (say, the wind).  His arrows all end up within two inches of each other, but off centre by six inches.  Average his shots, and the average is six inches away from the target.  You would say this archer had a high level of precision, but a low level of accuracy.  You could also say that his innacuracy was caused by experimental error.

A third archer, is as good as the second, but takes the wind into account.  his arrows all end up within two inches of the centre.  you would say he had a high level of both accuracy and precision.  He also had less experimental error than archer 2.

Answer 2

If you say that a person is 873.21 nanometers tall, you have a lot of precision (5 digits), but very little accuracy.   If you say he is 0.8 meters tall, you have little precision (1 digit) but lots of accuracy (if he really is 0.8 meters).

Answer 3

I got this bit of info from geek.com

"If the actual value is 4.321 and you say that it is 4.30, then you are precise to the first decimal place but inaccurate by .021. If a value is represented as a bulls-eye on a target, a group of guesses or measurements represented by closely grouped points have a high degree of precision. If that group is near the center, it is highly accurate as well. On a bullseye, think of accuracy as how close to the center your arrow hits, and your measurement of precision as how closely you can group your shots."

Just type accuracy vs precision into google search and there are lots of great examples to illustrate the difference.

Hope this helps!