Table 2.

Summary of mean kappa values for different components influencing the reproducibility of BKV IHC^1,2

	Combined Score3	Intensity-Only Score4	Percent-Only Score4	Positive vs. Negative5
Inter-institutional reproducibility: Variation between institutions resulting from differences in laboratory procedures plus subjective interpretation by different observers. Mean kappa values were calculated by comparing the scores provided by each participant on their locally-stained slide to the corresponding scores provided by the local participant from the center that produced the reference slide (n=81).	0.25 (0.23–0.27)	0.49 (0.44–0.54)	0.42 (0.37–0.47)	0.63 (0.58–0.68)
Inter-laboratory reproducibility: Variation resulting from differences in laboratory procedures. Mean kappa values were calculated by comparing the panel consensus scores for each slide to the panel consensus scores for the reference slide (n=48).	0.24 (0.21–0.27)	0.37 (0.32–0.42)	0.40 (0.33–0.47)	0.67 (0.63–0.71)
Inter-observer reproducibility: Variation resulting from subjective interpretation by different observers. Mean kappa values were calculated by comparing the scores of each local participant to the panel consensus scores on the same slide (n=59).	0.43 (0.38–0.48)	0.74 (0.68–0.80)	0.66 (0.60–0.72)	0.78 (0.72–0.84)

¹Significance of kappa values: <0 no agreement (or less than expected by chance), 0–0.20 slight, 0.21–0.40 fair, 0.41–0.60 moderate, 0.61–0.80 substantial, and 0.81–1.00 almost perfect agreement.

²Data is presented as mean and 95% confidence interval.

³Combined score is presented as Cohen’s kappa statistics (weighted kappa is not applicable as it is non-linear).

⁴Intensity-only and percent-only scores are presented as weighted kappa statistics.

⁵Positive (any staining) vs. negative (no staining) score is presented as Cohen’s kappa statistics.