

corCompSymm(nlme)                            R Documentation

_C_o_m_p_o_u_n_d _S_y_m_m_e_t_r_y _C_o_r_r_e_l_a_t_i_o_n _S_t_r_u_c_t_u_r_e

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

     This function is a constructor for the `corCompSymm'
     class, representing a compound symmetry structure cor-
     responding to uniform correlation. Objects created
     using this constructor must later be initialized using
     the appropriate `initialize' method.

_U_s_a_g_e_:

     corCompSymm(value, form, fixed)

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

   value: the correlation between any two correlated obser-
          vations. Defaults to 0.

    form: a one sided formula of the form `~ t', or `~ t |
               g', specifying a time covariate `t' and,
          optionally, a grouping factor `g'. When a grouping
          factor is present in `form', the correlation
          structure is assumed to apply only to observations
          within the same grouping level; observations with
          different grouping levels are assumed to be uncor-
          related. Defaults to `~ 1', which corresponds to
          using the order of the observations in the data as
          a covariate, and no groups.

   fixed: an optional logical value indicating whether the
          coefficients should be allowed to vary in the
          optimization, or kept fixed at their initial
          value. Defaults to `FALSE', in which case the
          coefficients are allowed to vary.

_V_a_l_u_e_:

     an object of class `corCompSymm', representing a com-
     pound symmetry correlation structure.

_A_u_t_h_o_r_(_s_)_:

     Jose Pinheiro and Douglas Bates

_R_e_f_e_r_e_n_c_e_s_:

     Milliken, G. A. and Johnson, D. E. (1992) "Analysis of
     Messy Data, Volume I: Designed Experiments", Van Nos-
     trand Reinhold.

_S_e_e _A_l_s_o_:

     `initialize.corStruct'

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

     library(nlme)
     ## covariate is observation order and grouping factor is Subject
     cs1 <- corCompSymm(0.5, form = ~ 1 | Subject)

