Table 1. . Early phase biomarker test analytical validation definitions and recommendations.

Validation factor	Definition	Supporting information
Accuracy	“The closeness of agreement between the test results obtained using the new biomarker test and results obtained using a reference standard method widely accepted as producing ‘truth’ for the analyte… The observed level of agreement will depend on both the bias and precision of the new test” [26]	– Fully describe the reference standard. When no reference standard exists, describe the nonreference standard employed– Describe the type and source of the samples (e.g., patient samples vs contrived, number of samples that are positive or negative for the clinical condition of interest) – Describe summary measures for the study (scatter plots, average bias, mean squared deviation for continuous data; 2 × 2 tables, overall percent agreement, sensitivity and specificity for binary data) and maintain raw data – Measurements of precision are discussed below[26]
Bias	“The amount by which an average of many repeated measurements made using the new test systematically over- or underestimates the reference standard method result” [26]
Repeatability	Precision of the biomarker test under essentially unchanged conditions (‘within-series precision’ or ‘within-run precision’) [26]	– Describe the study design (number of replicates, number of samples, number of factors considered and number of that factor included, range of assay values studied) – Describe the type and source of the samples (e.g., patient samples vs contrived, number of samples that are positive or negative for the clinical condition of interest) – Describe summary measures for each sample (mean, SD and CV% for continuous data; overall, positive and negative percent agreement for binary data) and maintain raw data. Test results should be summarized according to the output that will be used in the trial. Binary tests with underlying quantitative or semiquantitative data (e.g., imaging tests) should also provide quantitative or semiquantitative analyses when possible [26]
Intermediate precision	Precision of the biomarker test when there is “variation in one or more factors, such as time, calibration, operator and equipment – usually within a laboratory” [26]
Reproducibility	Precision of the biomarker test between laboratories that also “relates to changes in conditions such as different operators and measuring systems (including different calibrations and reagent batches)” [26]
LoD	“The smallest amount of analyte that an analytical method can detect with a specified probability” [26]	- Further discussion of LoD can be found elsewhere [27,28]
LoQ	“The smallest amount of an analyte in a sample that can be quantitatively determined with acceptable precision, and trueness as measured by bias” [26]	- Further discussion of LoQ can be found elsewhere [27,28]
Linearity	“The ability to provide measured quantity values that are directly proportional to the value of the measurand in the experimental unit” [28]	- Further discussion of linearity can be found elsewhere [28,29]

LoD: Limit of detection; LoQ: Limit of quantitation.