corCompSymm               package: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 corresponding 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 observations.
          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
          uncorrelated. 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 compound 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 Nostrand Reinhold.

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

     `initialize.corStruct'

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

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

