Accuracy vs. Precision: What's the Difference?

Accuracy and Precision:

Accuracy refers to the closeness of a measured value to a standard or known value. For example, if in lab you obtain a weight measurement of 3.2 kg for a given substance, but the actual or known weight is 10 kg, then your measurement is not accurate.

Accuracy 用来描述观测值与标准值的差异。例如，在实验室中，你对一个已知10kg的物体，测得的结果是3.2kg，那么你的结果是不准确的（not accurate）。

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Precision refers to the closeness of two or more measurements to each other. Using the example above, if you weigh a given substance five times, and get 3.2 kg each time, then your measurement is very precise. Precision is independent of accuracy. You can be very precise but inaccurate, as described above. You can also be accurate but imprecise.

Precision 用来描述两个或多个观测值相互之间的差异。就上例而言，如果你测了五次，每次测得的结果都是3.2kg，那么你的结果是非常精确的（very precise）。Precision 和 Accuracy 是相互独立的，就像刚刚的例子一样，你可以非常 precise 但一点儿也不 accurate， 也可以非常 accurate 而不 precise。

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For example, if on average, your measurements for a given substance are close to the known value, but the measurements are far from each other, then you have accuracy without precision.

例如，你的观测值在平均结果下和已知的标准值很接近，但每次的观测都各自差异很大，那么你就有了 accuracy 但是没有 precision。

Accuracy(left) and Precision(right):

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-- Reprinted from labwrite.ncsu.edu