3.7.2. Uncertainty of the mean of each method (repeatability of measurements)
Since more than one analytical method will be compared to determine the certified value, it is important that the variability of the mean for each method is estimated correctly. In order to estimate the standard uncertainty of the mean, ANOVA was used to determine which design factors have statistically significant effect on the measurements [14]. A two-way fully nested ANOVA model was used to perform data analysis, which reads as follows: