Linearity Analysis

Linearity analysis involves using an assay to test approximately 6–11 samples, preferably with multiple replicates of each specimen. This type of analysis assesses three assay performance metrics: accuracy, linearity, and reportable range. The acceptance criteria for these parameters should be defined before beginning an experiment. For example, the acceptable parameters for accuracy are defined in terms of total allowable error, which is comprised of two components: systematic error and random error. While these error components can be individually predefined, doing so is not necessarily required. For the assay’s reportable range, the acceptable parameters should reflect the device’s analytical range. The degree of linearity of the assay results can be predefined by an acceptable goodness-of-fit statistical test range. However, as indicated in the CLSI guidelines in document EP6, using the rule of thumb, “if it looks like a straight line,” is also adequate.⁷ In general, the pass-fail criteria for the assay performance metrics involve assessing whether the results are sufficiently close to the predefined acceptance level.