secalonic                package:drc                R Documentation

_R_o_o_t _l_e_n_g_t_h _m_e_a_s_u_r_e_m_e_n_t_s

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

     Data stem from an experiment assessing the inhibitory effect of
     secalonic acids on plant growth.

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

     data(secalonic)

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

     A data frame with 7 observations on the following 2 variables:

     '_d_o_s_e' a numeric vector containing dose values (mM)

     '_r_o_o_t_l' a numeric vector containing root lengths (cm)

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

     For each dose the root length is an average three measurements.

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

     Gong, X. and Zeng, R. and Luo, S. and Yong, C. and Zheng, Q.
     (2004) Two new  secalonic acids from _Aspergillus Japonicus_ and
     their allelopathic effects on higher plants, _Proceedings of
     International Symposium on Allelopathy Research and Application,
     27-29 April,  Shanshui, Guangdong, China (Editors: R. Zeng and S.
     Luo)_, 209-217.

     Ritz, C (2009) Towards a unified approach to dose-response
     modeling in ecotoxicology _To appear in Environ Toxicol Chem_.

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

     ## Fitting a four-parameter log-logistic model
     secalonic.m1 <- drm(rootl ~ dose, data = secalonic, fct = LL.4())
     summary(secalonic.m1)

     ## Fitting a three-parameter log-logistic model
     ##  lower limit fixed at 0
     secalonic.m2 <- drm(rootl ~ dose, data = secalonic, fct = LL.3())
     summary(secalonic.m1)

     ## Comparing logistic and log-logistic models
     ## (Figure 1 in Ritz (2009))
     secalonic.LL4 <- drm(rootl ~ dose, data = secalonic, fct = LL.4())
     secalonic.L4 <- drm(rootl ~ dose, data = secalonic, fct = L.4())

     plot(secalonic.LL4, broken=TRUE, ylim=c(0,7), xlab="Dose (mM)", ylab="Root length (cm)", 
     cex=1.2, cex.axis=1.2, cex.lab=1.2, lwd=2)

     plot(secalonic.L4, broken=TRUE, ylim=c(0,7), add=TRUE, type="none", lty=2, lwd=2)

     abline(h=coef(secalonic.L4)[3], lty=3, lwd=2)

