wheat                  package:gnm                  R Documentation

_W_h_e_a_t _Y_i_e_l_d_s _f_r_o_m  _M_e_x_i_c_a_n _F_i_e_l_d _T_r_i_a_l_s

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

     Data from a 10-year experiment at the CIMMYT experimental station
     located in the Yaqui Valley near Ciudad Obregon, Sonora, Mexico -
     factorial design using 24 treatments in all.  In each of the 10
     years the experiment was  arranged in a randomized complete block
     design with three replicates.

_U_s_a_g_e:

     data(wheat)

_F_o_r_m_a_t:

     A data frame with 240 observations on the following 33 variables.

     _y_i_e_l_d numeric, mean yield in kg/ha for 3 replicates

     _y_e_a_r a factor with levels '1988:1997'

     _t_i_l_l_a_g_e a factor with levels 'T' 't'

     _s_u_m_m_e_r_C_r_o_p a factor with levels 'S' 's'

     _m_a_n_u_r_e a factor with levels 'M' 'm'

     _N a factor with levels '0' 'N' 'n'

     _M_T_D numeric, mean max temp sheltered (deg C) in December

     _M_T_J same for January

     _M_T_F same for February

     _M_T_M same for March

     _M_T_A same for April

     _m_T_D numeric, mean min temp sheltered (deg C) in December

     _m_T_J same for January

     _m_T_F same for February

     _m_T_M same for March

     _m_T_A same for April

     _m_T_U_D numeric, mean min temp unsheltered (deg C)in December

     _m_T_U_J same for January

     _m_T_U_F same for February

     _m_T_U_M same for March

     _m_T_U_A same for April

     _P_R_D numeric, total precipitation (mm) in December

     _P_R_J same for January

     _P_R_F same for February

     _P_R_M same for March

     _S_H_D numeric, mean sun hours in December

     _S_H_J same for January

     _S_H_F same for February

     _E_V_D numeric, total evaporation (mm) in December

     _E_V_J same for January

     _E_V_F same for February

     _E_V_M same for March

     _E_V_A same for April

_S_o_u_r_c_e:

     Tables A1 and A3 of Vargas, M, Crossa, J, van Eeuwijk, F, Sayre, K
     D and Reynolds, M P (2001).  Interpreting treatment by environment
     interaction in agronomy trials.  _Agronomy Journal_ *93*, 949-960.

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

     set.seed(1)
     data(wheat)

     ##  Scale yields to reproduce analyses reported in Vargas et al (2001)
     yield.scaled <- wheat$yield * sqrt(3/1000)

     ##  Reproduce (up to error caused by rounding) Table 1 of Vargas et al (2001)
     aov(yield.scaled ~ year*tillage*summerCrop*manure*N, data = wheat)
     treatment <- interaction(wheat$tillage, wheat$summerCrop, wheat$manure,
                              wheat$N, sep = "")
     mainEffects <- glm(yield.scaled ~ year + treatment, family = gaussian,
                        data = wheat)
     bilinear1 <- gnm(yield.scaled ~ year + treatment + Mult(year, treatment),
                      family = gaussian, data = wheat)
     anova(mainEffects, bilinear1)
     ## Not run: 
         ## The next two take a lot of iterations to converge...
         bilinear2 <- gnm(yield.scaled ~ year + treatment +
                          Mult(year, treatment, multiplicity = 2),
                          family = gaussian, data = wheat)
         bilinear3 <- gnm(yield.scaled ~ year + treatment +
                          Mult(year, treatment, multiplicity = 3),
                          family = gaussian, data = wheat)
         anova(mainEffects, bilinear1, bilinear2, bilinear3)
     ## End(Not run)

     ##  Examine the extent to which, say, mTF explains the first bilinear term
     bilinear1mTF <- gnm(yield.scaled ~ year + treatment + Mult(1 + mTF, treatment),
                         family = gaussian, data = wheat)
     anova(mainEffects, bilinear1mTF, bilinear1)

