On Semi‐Parametric Models in Occult Tumour Experiments

Nonparametric statistical analyses of rodent carcinogenicity experiments involving occult tumours of intermediate lethality require numerous interim sacrifices. In recent papers, various semi‐parametric analyses have been proposed which specify a parametric relationship between the death rate in tumour‐bearing and tumour‐free animals as a means of relaxing the requirement for multiple interim sacrifices. These semi‐parametric methods involve different combinations of discrete and continuous time scales for the death and tumour‐onset processes. The effect of combining different scales on this parametric relationship is studied further and illustrated via an example.