Accuracy and Precision Definitions

Accuracy is a description of how close the result is to the true value. In the analogy of a dartboard, accurate results will the those closest to the bullseye.

Precision is a description of how close a result is to repeated results of the same test. On a dartboard, precise results will all the clustered together, though not necessarily close to the bullseye.

The tolerance of results is a description of the inherent variation of the method that is allowed and the product to still be within QC specification.

The limit of detection or LOD is the lowest concentration of analyte (the thing you are measuring) that you can reliably say is different from the blank.

The limit of quantification/quantitation or LOQ is the lowest concentration where you can be sure of the accuracy of the measurement. As at the lowest end of the range of a test, the variability will be higher than in the middle of the measurement range, the LOQ will always be higher than the LOD.

The method detection limit or MDL is a measure of the lowest concentration that can be detected using the exact method. This takes into account the instrument as well as the chemistry and is more representative of what a customer can expect to achieve.

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