Accuracy and Precision how they differ
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| Precision |
| Precision describes the consistency of a series of measurements. It has nothing to do with accuracy. Good precision simply tells how well a series of measurements cluster around the average result. The precision is good in Figure 3 and Figure 4. The precision is poor in Figure 1 and Figure 2. |
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| Accuracy |
Accuracy is a measure of the agreement between an accepted true value and and a measured result. The accuracy will be good if the result of an average value is close to the accepted value.Close is of course subjective and depends on how high expectations are. For example if you expect to get 95% on a test or assignment and you got 93%, then you would probably say the agreement was okay. On the other hand if you expected 95% and got 62%, then you would probably say the agreement was poor. Figure 2 and Figure 4 illustrate good accuracy. Figure 4 has both good accuracy and good precision. We want to hit the 'bulls eye' on average. If the average value is close to the 'bulls eye', then we have good accuracy. In Figure 2 the precision is poor. The darts are spread around the target, but the average location is near the center. The darts never hit the center, but average falls near it. |
