Three null hypotheses can be tested: linearity of time-dependence (b j2 = 0); lack of any of time-dependence, monotone or non-monotone (b j1 = b j2 = 0), and the lack of effect of covariate z_j on survival (b _j0 = b _j1 = b _j2 = 0)

A confidence band for b can be estimated .