mecter                  package:drc                  R Documentation

_M_e_c_h_l_o_r_p_r_o_p _a_n_d _t_e_r_b_y_t_h_y_l_a_z_i_n_e _t_e_s_t_e_d _o_n _L_e_m_n_a _m_i_n_o_r

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

     Data consist of 5 mixture, 6 dilutions, three replicates, and 12
     common controls; in total 102 onservations.

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

     data(mecter)

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

     A data frame with 102 observations on the following 3 variables.

     '_d_o_s_e' a numeric vector of dose values

     '_p_c_t' a numeric vector denoting the grouping according to the
          mixtures percentages

     '_r_g_r' a numeric vector of response values (relative growth rates)

_D_e_t_a_i_l_s:

     The dataset is analysed in Soerensen et al (2007).  The asymmetric
     Voelund model is appropriate, whereas the symmetric Hewlett model
     is not.

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

     The dataset is kindly provided by Nina Cedergreen, Department of
     Agricultural Sciences,  Royal Veterinary and Agricultural
     University, Denmark.

_R_e_f_e_r_e_n_c_e_s:

     Soerensen, H. and Cedergreen, N. and Skovgaard, I. M. and
     Streibig, J. C. (2007)  An isobole-based statistical model and
     test for synergism/antagonism in binary mixture toxicity
     experiments,  _Environmental and Ecological Statistics_, *14*,
     383-397.

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

     ## Fitting the model with freely varying ED50 values
     mecter.free <- drm(rgr ~ dose, pct, data = mecter, 
     fct = LL.4(), pmodels = list(~1, ~1, ~1, ~factor(pct) - 1)) 

     ## Lack-of-fit test
     modelFit(mecter.free)  # not really acceptable
     summary(mecter.free)

     ## Plotting isobole structure
     isobole(mecter.free, exchange = 0.02)

     ## Fitting the concentration addition model
     mecter.ca <- mixture(mecter.free, model = "CA")

     ## Comparing to model with freely varying e parameter
     anova(mecter.ca, mecter.free)  # rejected

     ## Plotting isobole based on concentration addition
     isobole(mecter.free, mecter.ca, exchange = 0.02)  # poor fit

     ## Fitting the Hewlett model
     mecter.hew <- mixture(mecter.free, model = "Hewlett")

     ## Comparing to model with freely varying e parameter
     anova(mecter.hew, mecter.free)  # rejected

     ## Plotting isobole based on the Hewlett model
     isobole(mecter.free, mecter.hew, exchange = 0.02)  # poor fit

     ## Fitting the Voelund model
     mecter.voe<-mixture(mecter.free, model = "Voelund")

     ## Comparing to model with freely varying e parameter
     anova(mecter.voe, mecter.free)  # accepted

     ## Plotting isobole based on the Voelund model
     isobole(mecter.free, mecter.voe, exchange = 0.02)  # good fit

