accuracy：準確
precision：精確
Accuracy and precision are two important factors to consider when taking data measurements. Both accuracy and precision reflect how close a measurement is to an actual value, but accuracy reflects how close a measurement is to a known or accepted value, while precision reflects how reproducible measurements are, even if they are far from the accepted value.
Accuracy vs Precision
- Accuracy is how close a value is to its true value. An example is how close an arrow gets to the bull's-eye center.
- Precision is how repeatable a measurement is. An example is how close a second arrow is to the first one (regardless of whether either is near the mark).
- Percent error is used to assess whether a measurement is sufficiently accurate and precise.
Accuracy
There are two common definitions of accuracy. In math, science, and engineering, accuracy refers to how close a measurement is to the true value.
The ISO (International Organization for Standardization) applies a more rigid definition, where accuracy refers to measurement with both true and consistent results. The ISO definition means an accurate measurement has no systematic error and no random error. Essentially, the ISO advises that accurate be used when a measurement is both accurate and precise.
Precision
Precision is how consistent results are when measurements are repeated. Precise values differ from each other because of random error, which is a form of observational error.
Examples
You can think of accuracy and precision in terms of a basketball player. If the player always makes a basket, even though he strikes different portions of the rim, he has a high degree of accuracy. If he doesn't make many baskets but always strikes the same portion of the rim, he has a high degree of precision. A player whose free throws always make the basket the exact same way has a high degree of both accuracy and precision.
Take experimental measurements for another example of precision and accuracy. If you take measurements of the mass of a 50.0-gram standard sample and get values of 47.5, 47.6, 47.5, and 47.7 grams, your scale is precise, but not very accurate. If your scale gives you values of 49.8, 50.5, 51.0, and 49.6, it is more accurate than the first balance but not as precise. The more precise scale would be better to use in the lab, providing you made an adjustment for its error.
Mnemonic to Remember the Difference
An easy way to remember the difference between accuracy and precision is:
- ACcurate is Correct (or Close to real value)
- PRecise is Repeating (or Repeatable)