(1) In addition, mishandling due to the high viscosity of saliva can make pipetting especially difficult.
Salimetrics offers the following comments on calculating and interpreting CVs: (1) An illustration of the calculation of the intra-assay CV from 40 samples (using internal Salimetrics data) is provided in Example 2. The intra-assay CV reported in these studies is an average value calculated from the individual CVs for all of the duplicates, even if the total number of samples requires the use of multiple assay plates. Testing each sample with greater numbers of replicates would produce statistically better results for the standard deviation and calculation of the CV, but this practice would be prohibitively expensive for large studies.
The degree to which the duplicate results differ can be expressed by calculating the standard deviation of the two results and converting it to the CV. Most studies measure each sample in duplicate for each analyte. The inter-assay CV is an expression of plate-to-plate consistency that is calculated from the mean values for the high and low controls on each plate, as illustrated in Example 1 below (taken from internal Salimetrics data). Each plate is run with its own calibrators for the standard curve, and saliva controls with known concentrations of the analyte–usually a high and a low value–are also included on each plate. In larger studies with many samples to be tested, it is necessary that samples be run on multiple assay plates. Since the usage of the term intra-assay CV may vary somewhat between fields of study, some clarification of terminology and methods is in order. The CV is a dimensionless number defined as the standard deviation of a set of measurements divided by the mean of the set. In order to express the precision, or repeatability, of immunoassay test results, researchers in the social and behavioral sciences typically report two measures of the Coefficient of Variability (CV) in their publications: the Inter-Assay CV and the Intra-Assay CV.