Fig. 4

Method performance across laboratories and products. (a) Z-score distribution of each laboratory’s bias relative to the mean of all laboratories (excluding outlier values) for each product assayed at 37 °C. Each point represents one product by an individual laboratory. Horizontal line indicates reference (z = 0), the highlighted area where |z|≤ 2 indicates satisfactory performance, areas where |z|≥ 2 and |z|≤ 3 indicate unsatisfactory performance. (b) Repeatability (CV_r, %) for each laboratory and product. (c) Reproducibility (CV_R, %) among all laboratories, excluding outliers, for each product. Colour/Marker shape coding: blue/circle – saliva; green/triangle – Porcine pancreatin; orange/diamond—α-amylase M; pink – α-amylase S.