NEC                   package:drc                   R Documentation

_D_o_s_e-_r_e_s_p_o_n_s_e _m_o_d_e_l _f_o_r _e_s_t_i_m_a_t_i_o_n _o_f _n_o _e_f_f_e_c_t _c_o_n_c_e_n_t_r_a_t_i_o_n (_N_E_C).

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

     The no effect concentration has been proposed as an alternative to
     both the classical no observed effect concentration (NOEC) and the
     regression-based EC/ED approach. The NEC model is a dose-response
     model with a threshold below  which the response is assumed
     constant and equal to the control response.

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

       NEC(fixed = c(NA, NA, NA, NA), names = c("b", "c", "d", "e"), fctName, fctText)

       NEC.2(upper = 1, fixed = c(NA, NA), names = c("b", "e"), ...)
       
       NEC.3(fixed = c(NA, NA, NA), names = c("b", "d", "e"), ...)
       
       NEC.4(fixed = c(NA, NA, NA, NA), names = c("b", "c", "d", "e"), ...)

_A_r_g_u_m_e_n_t_s:

   fixed: numeric vector specifying which parameters are fixed and at
          what value they are fixed.  NAs are used for parameters that
          are not fixed.

   names: a vector of character strings giving the names of the
          parameters (should not contain ":"). The default is
          reasonable (see under 'Usage').

 fctName: optional character string used internally by convenience
          functions.

 fctText: optional character string used internally by convenience
          functions.

   upper: numeric value. The fixed, upper limit in the model. Default
          is 1.

     ...: additional arguments in 'NEC'

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

     The NEC model function proposed by Pires _et al_ (2002) is defined
     as follows


 f(x) = c + (d-c)exp(-b(x-e)I(x-e)) + frac{d2}{1+exp(b2(log(x)-log(e2)))}


     where I(x-e) is the indicator function. It is equal to 0 for x<=e
     and equal 1 for x>e

_V_a_l_u_e:

     The value returned is a list containing the nonlinear function,
     the self starter function and the parameter names.

_A_u_t_h_o_r(_s):

     Christian Ritz

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

     Pires, A. M., Branco, J. A., Picado, A., Mendonca, E. (2002)
     Models for the estimation of a 'no effect concentration',
     _Environmetrics_, *13*, 15-27.

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

     nec.m1 <- drm(rootl~conc, data=ryegrass, fct=NEC.4())

     summary(nec.m1)

     plot(nec.m1)

