

boxcox(MASS)                                 R Documentation

_B_o_x_-_C_o_x _T_r_a_n_s_f_o_r_m_a_t_i_o_n_s _f_o_r _L_i_n_e_a_r _M_o_d_e_l_s

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

     Computes and optionally plots profile log-likelihoods
     for the parameter of the Box-Cox simple power transfor-
     mation `y^lambda'.

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

     boxcox(model, lambda, plotit, interp, eps, xlab, ylab, ...)

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

   model: a formula or fitted model object.  Currently only
          `lm' and `aov' objects are handled.

  lambda: vector of values of `lambda' - default (-2, 2) in
          steps of 0.1

  plotit: logical which controls whether the result should
          be plotted.  Default to `true' if a graphics
          device is currently open.

  interp: logical which controls whether spline interpola-
          tion is used.  Default to `true' if plotting with
          `lambda' of length less than 100.

     eps: Tolerance for `lambda = 0'; defaults to 0.02

    xlab: defaults to `"lambda"'

    ylab: defaults to `"log-Likelihood"'

     ...: additional parameters to be used in the model fit-
          ting.

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

     A list of the `lambda' vector and the computed profile
     log-likelihood vector, invisibly if the result is plot-
     ted.

_S_i_d_e _E_f_f_e_c_t_s_:

     If `plotit = TRUE' plots loglik vs `lambda' and indi-
     cates a 95% confidence interval about the maximum
     observed value of `lambda'. If `interp = TRUE', spline
     interpolation is used to give a smoother plot.

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

     data(trees)
     boxcox(Volume ~ log(Height) + log(Girth), data = trees,
            lambda = seq(-0.25, 0.25, length = 10))
     data(quine)
     boxcox(Days+1 ~ Eth*Sex*Age*Lrn, data = quine, singular.ok = TRUE,
      lambda = seq(-0.05, 0.45, len = 20))

