Spruce package:nlme R Documentation _G_r_o_w_t_h _o_f _S_p_r_u_c_e _T_r_e_e_s _D_e_s_c_r_i_p_t_i_o_n: The 'Spruce' data frame has 1027 rows and 4 columns. _F_o_r_m_a_t: This data frame contains the following columns: _T_r_e_e a factor giving a unique identifier for each tree. _d_a_y_s a numeric vector giving the number of days since the beginning of the experiment. _l_o_g_S_i_z_e a numeric vector giving the logarithm of an estimate of the volume of the tree trunk. _p_l_o_t a factor identifying the plot in which the tree was grown. _D_e_t_a_i_l_s: Diggle, Liang, and Zeger (1994, Example 1.3, page 5) describe data on the growth of spruce trees that have been exposed to an ozone-rich atmosphere or to a normal atmosphere. _S_o_u_r_c_e: Pinheiro, J. C. and Bates, D. M. (2000), _Mixed-Effects Models in S and S-PLUS_, Springer, New York. (Appendix A.28) Diggle, Peter J., Liang, Kung-Yee and Zeger, Scott L. (1994), _Analysis of longitudinal data_, Oxford University Press, Oxford.