lettuce                 package:drc                 R Documentation

_I_s_o_b_u_t_y_l_a_l_c_o_h_o_l _i_n _n_u_t_r_i_e_n_t _s_o_l_u_t_i_o_n _i_n _w_h_i_c_h _l_e_t_t_u_c_e _p_l_a_n_t_s _w_e_r_e _g_r_o_w_n

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

     Data are from an experiment where isobutylalcohol was dissolved in
     a nutrient solution in which lettuce (_Lactuca sativa_) plants
     were grown. The plant biomass of the shoot was determined af 21
     days.

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

     data(lettuce)

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

     A data frame with 14 observations on the following 2 variables.

     _c_o_n_c a numeric vector of concentrations of isobutylalcohol (mg/l)

     _w_e_i_g_h_t a numeric vector of biomass of shoot (g)

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

     The data set illustrates hormesis, presence of a subtoxic stimulus
     at low concentrations.

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

     van Ewijk, P. H. and Hoekstra, J. A. (1993)  Calculation of the
     EC50 and its Confidence Interval When Subtoxic Stimulus Is
     Present, _ECOTOXICOLOGY AND ENVIRONMENTAL SAFETY_, *25*, 25-32.

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

     van Ewijk, P. H. and Hoekstra, J. A. (1994)  Curvature Measures
     and Confidence Intervals for the Linear Logistic Model, _Appl.
     Statist._, *43*, 477-487.

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

     ## Look at data
     lettuce

     ## Monotonous dose-response model
     lettuce.m1 <- drm(weight~conc, data=lettuce, fct=LL.3())

     plot(lettuce.m1, broken = TRUE)

     ## Model fit in van Ewijk and Hoekstra (1994)
     lettuce.m2 <- drm(weight~conc, data=lettuce, fct=BC.4())
     modelFit(lettuce.m2)

     plot(lettuce.m2, add = TRUE, broken = TRUE, type = "none", lty = 2)

     ## Hormesis effect only slightly significant
     summary(lettuce.m2)

     ## Hormesis effect highly significant
     ##  compare with t-test
     anova(lettuce.m1, lettuce.m2)

