Sitka package:MASS R Documentation _G_r_o_w_t_h _C_u_r_v_e_s _f_o_r _S_i_t_k_a _S_p_r_u_c_e _T_r_e_e_s _i_n _1_9_8_8 _D_e_s_c_r_i_p_t_i_o_n: The 'Sitka' data frame has 395 rows and 4 columns. It gives repeated measurements on the log-size of 79 Sitka spruce trees, 54 of which were grown in ozone-enriched chambers and 25 were controls. The size was measured five times in 1988, at roughly monthly intervals. _U_s_a_g_e: Sitka _F_o_r_m_a_t: This data frame contains the following columns: '_s_i_z_e' measured size (height times diameter squared) of tree, on log scale. '_T_i_m_e' time of measurement in days since 1 January 1988. '_t_r_e_e' number of tree. '_t_r_e_a_t' either '"ozone"' for an ozone-enriched chamber or '"control"'. _S_o_u_r_c_e: P. J. Diggle, K.-Y. Liang and S. L. Zeger (1994) _Analysis of Longitudinal Data._ Clarendon Press, Oxford _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: 'Sitka89'.