Accuracy and precision

Accuracy is how close a measurement is to a true or accepted value; precision is how closely repeated measurements agree with one another.

Measurement uncertainty: A quantified range or distribution expressing doubt about a measurement result. It describes the uncertainty that remains even when measurements are precise.
Systematic error: An error component that remains constant or changes predictably across repeated measurements. It shifts results consistently away from the reference, harming accuracy.
Analytical chemistry: The branch of chemistry that identifies substances and determines their amounts. Chemical assays evaluate both closeness to reference concentrations and run-to-run consistency.
Trueness: The closeness of the average of repeated measurements to a reference value. It isolates the accuracy component associated with systematic deviation.
Measurement error: The difference between a measured value and a reference value. Its systematic and random components affect accuracy and precision differently.
Random error: An unpredictable error component that varies across repeated measurements. It creates scatter and limits precision even when average results are accurate.
Quality control: Methods used to monitor whether products or processes meet defined requirements. Control charts detect shifts in accuracy and changes in measurement spread.
Reproducibility: The closeness of results obtained under changed conditions, such as different laboratories or operators. It differs from precision assessed under unchanged conditions.
Calibration: Comparison of an instrument’s readings with known standards to establish or adjust its response. It can reveal and correct systematic offsets that reduce accuracy.
Bias (statistics): A systematic difference between an estimator’s expected value and the quantity it estimates. Measurement bias is one statistical expression of persistent inaccuracy.

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