  To claim similarity of multiple dose-response curves in interlaboratory
studies in regulatory toxicology is a relevant issue during the assay
validation process. Here we demonstrated the use of dose-by-laboratory
interaction contrasts, particularly Williams-type by total mean contrasts. With
the CRAN packages statint and multcomp in the open-source software R the
estimation of adjusted p-values or compatible simultaneous confidence intervals
is relatively easy. The interpretation in terms of global or partial
equivalence, i.e. similarity, is challenging, because thresholds are not
available a-priori. This approach is demonstrated by selected in-vitro Ames MPF
assay data.
