Intra-assay Variability of EIAs Commonly Used in the EQA Scheme (IgM).

<p>Mean (log S/CO) ± SD for all assays are given per sample. Absence of error bars means that the assay was used by less than 5 laboratories. SD below the dotted line at 0.0 refers to false-negative assay results. The S/CO values for all positive samples used by each assay showed a skewed distribution, therefore, the results were transformed to the log normal distribution for analysis (P-P plot).