Terminology Related to Testing and Inspection

Repeatability

Repeatability is the maximum difference between two independent single test results for the same sample, obtained by the same operator, in the same laboratory, using the same instrument, and within a short period, under normal and correct operating conditions, at a 95% probability level.

Reproducibility

Reproducibility refers to the degree of closeness between two analytical results for the same material measured by two different laboratories. The value for reproducibility is always greater than or equal to repeatability, because the reproducibility measurement takes into account the deviation caused by repeatability. In much of the practical work, the most important type of reproducibility refers to the consistency between repeated test results for the same measured object, obtained by different operators, using the same method and instrument, under the same environmental conditions, where the only change in test conditions is the operator.

Accuracy and Precision

Accuracy refers to the degree to which the average of multiple measurements conforms to the true value under certain experimental conditions, expressed as an error. It is used to represent the magnitude of systematic error.

Precision refers to the degree of consistency between measured values and their closeness to the "true value." It is a comprehensive concept of both precision and correctness. From the perspective of measurement error, precision is a comprehensive reflection of both the random error and systematic error of the measured value.

Standard Deviation (Std Dev)

A statistical term. It is a standard measure of the dispersion of a data distribution, used to measure the extent to which data values deviate from the arithmetic mean. The smaller the standard deviation, the less these values deviate from the mean, and vice versa. The magnitude of the standard deviation can be measured by its relationship with the average value as a multiple.

Relative Standard Deviation (RSD)

This refers to the ratio of the standard deviation to the arithmetic mean of the measurement results, that is: Relative Standard Deviation (RSD) = Standard Deviation (SD) / Arithmetic Mean of Calculated Results (X) * 100% This value is typically used to express the precision (精密度) of analytical test results.

Detection Limit

The detection limit is a common term in analytical chemistry. It is generally divided into instrument detection limit and method detection limit. The instrument detection limit refers to the ability of an analytical instrument to detect a small signal that can be distinguished from noise. The method detection limit is not only related to instrument noise but also depends on every step of the entire method process, such as sampling, separation and enrichment, and optimization of measurement conditions. That is to say, the analyst, environment, and sample properties all have an influence on the detection limit. In practical work, the specific conditions under which the detection limit was obtained should be stated.

In the past, the detection limit was also called the limit of detection, detection limit, determination limit, fluctuation concentration limit, etc. It is recommended to unify the term as "detection limit" for its brevity and intuitive nature.