Reliability and reproducibility of visual e-norms plateau identification

To derive normal values from a lab's own diagnostic studies, the e-norms method relies on the proper identification of the e-norms plateau to derive descriptive statistics of the variable under study. This work was undertaken to compare the inter and intra-rater reliability of visual identification of the plateau by different raters analyzing laboratory nerve conductions study data.

Twenty raters were asked to visually identify the inflection points delineating an e-norms plateau to derive the Mean value of nerve conduction study laboratory data while blinded to the parameter they were analyzing. After a delay of 1-3 months, the same raters were asked to repeat some of the e-norms plateaus identification to assess delayed intra-rater reproducibility.

Mean values derived from the identified plateau data were compared between raters (inter-rater) using a two factor ANOVA without replication. For the immediate inter-rater no statistically significant difference was found between the Means obtained by the different raters. For the delayed intra-rater, differences were found between raters.

This study suggests that visual identification of the e-norms plateau inflection point is reliable between raters but more research is needed to assess reproducibility for the same raters.

E-norms is a promising method for deriving reference values using data that is available in most electrophysiology laboratories.