acidiq                  package:drc                  R Documentation

_A_c_i_f_l_u_o_r_f_e_n _a_n_d _d_i_q_u_a_t _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 from an experiment where the chemicals acifluorfen and diquat
     tested on Lemna minor. The dataset has 7 mixtures used in 8
     dilutions with three replicates and 12 common controls, in total
     180 observations.

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

     data(acidiq)

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

     A data frame with 180 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).  Hewlett's
     symmetric model seems appropriate for this dataset.

_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
     ## Ooops: Box-Cox transformation is needed
     acidiq.free <- drm(rgr ~ dose, pct, data = acidiq, fct = LL.4(),
     pmodels = list(~factor(pct), ~1, ~1, ~factor(pct) - 1))

     ## Lack-of-fit test
     modelFit(acidiq.free)
     summary(acidiq.free)

     ## Plotting isobole structure
     isobole(acidiq.free, exchange = 0.1, xlim = c(0, 400), ylim = c(0,45))

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

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

     ## Plotting isobole based on concentration addition -- poor fit
     isobole(acidiq.free, acidiq.ca, exchange = 0.1, xlim = c(0, 420), ylim = c(0,45))  # poor fit

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

     ## Comparing to model with freely varying e parameter
     anova(acidiq.free, acidiq.hew)  # accepted
     summary(acidiq.hew)

     ## Plotting isobole based on the Hewlett model
     isobole(acidiq.free, acidiq.hew, exchange = 0.1, xlim = c(0, 400), ylim = c(0,45))  # good fit

