Appendix: Dose-response curve and plot symbols

The shape of the dose-response has been determined by a test for departure from linearity, the chi-square goodness-of-fit test (p<0.05).

Code	Dose-Response Curve	
*	Consistent with linearity	
/	Significant departure from linearity, upward curvature	
\	Significant departure from linearity, downward curvature.  In the plot, parentheses around the tumor incidence for a dose group indicate that the data were omitted from the final TD50 calculation.	
Z	Significant departure from linearity, more than three dose groups including controls	
	For \ and Z, if there was significant downward departure from linearity, the TD50 was calculated without the data from the highest dose groups(s).  In the plot, parentheses around the tumor incidence for a dose group indicate that the data were omitted from the final TD50 calculation.	
blank	Either no dose-related effect, or no curve shape could be determined because experiment had only two dose groups including controls	

Code	Plot symbol (appears once per experiment)	
:	TD50 estimated with lifetable data, and “:” indicates 99% confidence limits