contr.sdif               package:MASS               R Documentation

_S_u_c_c_e_s_s_i_v_e _D_i_f_f_e_r_e_n_c_e_s _C_o_n_t_r_a_s_t _C_o_d_i_n_g

_D_e_s_c_r_i_p_t_i_o_n:

     A coding for unordered factors based on successive differences.

_U_s_a_g_e:

     contr.sdif(n, contrasts = TRUE)

_A_r_g_u_m_e_n_t_s:

       n: The number of levels required. 

contrasts: Should there be 'n - 1' columns orthogonal to the mean (the
          default) or 'n' columns spanning the space. 

_D_e_t_a_i_l_s:

     The contrast coefficients are chosen so that the coded
     coefficients in a one-way layout are the differences between the
     means of the second and first levels, the third and second levels,
     and so on.

_V_a_l_u_e:

     If 'contrasts' is 'TRUE', a matrix with 'n' rows and 'n - 1'
     columns, and the 'n' by 'n' identity matrix if 'contrasts' is
     'FALSE'.

_R_e_f_e_r_e_n_c_e_s:

     Venables, W. N. and Ripley, B. D. (2002) _Modern Applied
     Statistics with S._ Fourth Edition, Springer.

_S_e_e _A_l_s_o:

     'contr.treatment', 'contr.sum', 'contr.helmert'.

_E_x_a_m_p_l_e_s:

     contr.sdif(6)

