3. Data Life Cycle

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3.4.2 Precision & Accuracy

one can be very precise but… also very inaccurate.

Often incorrectly used as synonyms, these two terms have very different meanings as illustrated by this diagram.

ISO standard 5725 1 refers to trueness as a better word for describing the principles and methods used for measuring and assessing the accuracy of a test. Trueness is defined as the degree of agreement between the arithmetic mean of a large number of test results and an accepted reference value; precision refers to the agreement between test results.

Data management errors are generally defined by their source:

  • human: errors in reading, typing, transcribing or in judgement;
  • environmental: errors due to ambiant conditions having an influence on measurements. E.g.: air temperature;
  • equipment: errors due to equipment limitations and/or capacities.

Errors can also be called "systemic" when they present similarities in occurrence and pattern ("bias" is also used) or, on the contrary, called "random" when no particular trend is detected.


  • Ensure staff is appropriately trained;
  • Perform quality control tests. E.g.: comparing measurements and observations to references.
  1. ISO 5725-1:1994. Accuracy (Trueness and Precision) of Measurement Methods and Results. https://www.iso.org/obp/ui/#iso:std:11833:en