I fitted tree growth data with Chapman-Richards growth function using nls. summary(CR) Formula: HEIGHT ~ A * (1 - exp(-B * AGE))^C Parameters: Estimate Std. Error t value Pr(>|t|) A 29.007627 0.270485 107.24 <2e-16 *** B 0.030813 0.001095 28.13 <2e-16 *** C 1.849405 0.068659 26.94 <2e-16 *** --- Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1 Residual standard error: 1.879 on 713 degrees of freedom Algorithm "port", convergence message: relative convergence (4) When I try to run the anova90 function I get this: anova(CR) Error in anova.nls(CR) : anova is only defined for sequences of "nls" objects Could you tell me what the problem is? Thanks Michael [[alternative HTML version deleted]]