## Accuracy

Accuracy is the degree of conformity of a measured or calculated quantity to its actual (true) value. Accuracy is closely related to precision, also called reproducibility or repeatability, the degree to which further measurements or calculations show the same or similar results. The results of calculations or a measurement can be accurate but not precise; precise but not accurate; neither; or both. Accuracy is the degree of veracity while precision is the degree of reproducibility. The analogy used here to explain the difference between accuracy and precision is the target comparison. In this analogy, repeated measurements are compared to arrows that are fired at a target. Accuracy describes the closeness of arrows to the bullseye at the target center. Arrows that strike closer to the bullseye are considered more accurate. The closer a system's measurements to the accepted value, the more accurate the system is considered to be. To continue the analogy, if a large number of arrows are fired, precision would be the size of the arrow cluster. When all arrows are grouped tightly together, the cluster is considered precise because they all struck close to the same spot, if not necessarily near the bullseye. The measurements are precise, though not necessarily accurate.

Data Attributes

Keith Reynolds

6/5/2008

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