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The excellent paper by Rhodes and colleagues1 provides a valuable insight into the factors that might cause interlaboratory variability in the immunohistochemical demonstration of oestrogen receptors, now probably the most frequent histopathology result that determines specific patient treatment.2 There is, however, one section of the paper where the statistical analysis may be causing confusion, rather than clarity.
In table 6, the degrees of agreement between the participant and organising laboratories for oestrogen receptor expression using the “Quick score” method are given. For each level of expression a κ statistic is given, and the values of all these statistics are less than zero, indicating a degree of agreement that is worse than chance alone. These κ statistics might be a reasonable reflection of the low levels of concordance, but it is unusual to calculate them for each level of expression, rather than all levels of expression together,3 and it is not clear which results have been included in each 2 × 2 contingency table to derive these statistics. A more usual way to assess the level of agreement would be to have a 4 × 4 contingency table with all levels of expression within …