Accuracy and Precision

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Presentation transcript:

Accuracy and Precision It’s all about the data

All measurements have an inherent error—instrument errors, method errors, or human error.

Accuracy The extent to which a measurement approaches the true value of a quantity (from Chemistry: Visualizing Matter) Accuracy is associated with measured values, for example, measurements of the concentration of a chemical in seawater. Accuracy is how close to the accepted or true value a measurement is. (from http://bell.mma.edu/~jbouch/Glossary/Accuracy.html)

Precision The degree of exactness or refinement of a measurement (from Chemistry: Visualizing Matter) A measure of the reproducibility of a particular measurement Gives information on the scale markings of the measuring instrument Communicated using “significant figures” Precision measures how far from the mean or average of replicate measurements a particular measurement lies. (from http://bell.mma.edu/~jbouch/Glossary/Accuracy.html)

Good accuracy, good precision x x x x x x

Good accuracy, poor precision x x x x x x x x

Precise, but not accurate x x x x x x x

Neither accurate nor precise x x x x x x