strata               package:survival5               R Documentation

_I_d_e_n_t_i_f_y _S_t_r_a_t_a _V_a_r_i_a_b_l_e_s

_D_e_s_c_r_i_p_t_i_o_n:

     This is a special function used in the context of the Cox survival
     model. It identifies stratification variables when they appear on
     the right hand side of a formula.

_U_s_a_g_e:

     strata(..., na.group=F)

_A_r_g_u_m_e_n_t_s:

     ...: any number of variables.  All must be the same length. 

na.group: a logical variable, if `TRUE', then missing values are
          treated as a distinct level of each variable. 

_D_e_t_a_i_l_s:

     The result is identical to the `interaction' function, but for the
     labeling of the factors (`strata' is more verbose).

_V_a_l_u_e:

     a new factor, whose levels are all possible combinations of the
     factors supplied as arguments.

_E_x_a_m_p_l_e_s:

     data(ovarian)
     coxph(Surv(futime, fustat) ~ age + strata(rx), data=ovarian)

