In eCerto: Statistical Tests for the Production of Reference Materials

Stability uncertainty calculation

The parameters of all linear models are collected in Tab.S1 and the potential uncertainty contribution of the material stability is obtained from formula $u_{stab}={|t_{cert} \times s(b_1)| \over \mu_s}$ where $t_{cert}$ is the expected shelf life of the CRM (in month) and $s(b_1)$ is the standard error SE of the slope of the linear model. $\mu_s$ is calculated as the mean of all values of an analyte depicted in Fig.S1, i.e. all values included in the linear model calculation.

The expected shelf life can be set by the user and should incorporate the time until the first certification monitoring and the certified shelf life of the material. This estimation of stability uncertainty is based on section 8.7.3 of ISO GUIDE 35:2017 and valid in the absence of a significant trend.

To determine if the slope $b_1$ is significantly different from $b_1=0$ we perform a t-test by calculating the t-statistic $t_m = |b_1| / s(b_1)$ and compare the result with the two-tailed critical value of Student's $t$ for $n - 2$ degrees of freedom to obtain the P-values in column P.

Note! Clicking on a table row will display the analysis for the analyte specified in this row.

Values from column u_stab_ can be transferred to a user defined column of the material table Tab.C3 in the certification module for matching analyte names. Analytes of Tab.S1 which can not be matched to Tab.C3 are depicted in red.

eCerto documentation built on April 12, 2025, 9:13 a.m.