Fig. 2. Study designs for linearity validation. (A) Design A (recommended): Intermediate samples are prepared by mixing high-level sample and blank sample (a straight line linear with no intercept); (B) Design B: Intermediate samples are prepared by mixing high-level sample and low-level sample (a straight line linear with a non-zero intercept).
RC (relative concentration): The relative ratio of the value of the intermediate sample compared to the value of the high-level sample. The RC of the high-level sample is 1, the RC of the blank sample is 0, and the RC of the intermediate sample prepared by mixing the high-level sample and blank sample in a volume of 1:1 is 0.5.
P_H (the proportion of high-level sample): The relative fraction of high-level sample in the intermediate sample. In an intermediate sample prepared by mixing a high-level sample and a low-level sample in a volume of 8:2, the value of the intermediate sample is calculated by Value(S)=0.8∙Value (H)+0.2∙Value(L). (Reprinted with permission from Clinical and Laboratory Standards Institute from: CLSI. Evaluation of Linearity of Quantitative Measurement Procedures. 2nd ed. CLSI guideline EP06. Clinical and Laboratory Standards Institute, 2020 [12]).

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