trees                package:datasets                R Documentation

_G_i_r_t_h, _H_e_i_g_h_t _a_n_d _V_o_l_u_m_e _f_o_r _B_l_a_c_k _C_h_e_r_r_y _T_r_e_e_s

_D_e_s_c_r_i_p_t_i_o_n:

     This data set provides measurements of the girth, height and
     volume of timber in 31 felled black cherry trees.  Note that girth
     is the diameter of the tree (in inches) measured at 4 ft 6 in
     above the ground.

_U_s_a_g_e:

     trees

_F_o_r_m_a_t:

     A data frame with 31 observations on 3 variables.

       '[,1]'  'Girth'   numeric  Tree diameter in inches
       '[,2]'  'Height'  numeric  Height in ft
       '[,3]'  'Volume'  numeric  Volume of timber in cubic ft

_S_o_u_r_c_e:

     Ryan, T. A., Joiner, B. L. and Ryan, B. F. (1976) _The Minitab
     Student Handbook_. Duxbury Press.

_R_e_f_e_r_e_n_c_e_s:

     Atkinson, A. C. (1985) _Plots, Transformations and Regression_.
     Oxford University Press.

_E_x_a_m_p_l_e_s:

     require(stats); require(graphics)
     pairs(trees, panel = panel.smooth, main = "trees data")
     plot(Volume ~ Girth, data = trees, log = "xy")
     coplot(log(Volume) ~ log(Girth) | Height, data = trees,
            panel = panel.smooth)
     summary(fm1 <- lm(log(Volume) ~ log(Girth), data = trees))
     summary(fm2 <- update(fm1, ~ . + log(Height), data = trees))
     step(fm2)
     ## i.e., Volume ~= c * Height * Girth^2  seems reasonable