奇怪的ED50与drc

Question

我正在尝试使用drc包估算IC50值。绘制模型的工作正常。但是当我使用ED时，我得到了不合理的结果。

根据我的理解，IC50应该在模型的拐点附近。在这种情况下，我估计大约0.25。但是ED将其计算为-1.43。 我是否使用ED错误或错过了什么？

由于

数据的小例子：

# Create Data
Conc <- c(0.03125, 0.06250, 0.12500, 0.25000, 0.50000, 1.00000, 0.03125, 0.06250, 0.12500, 0.25000, 0.50000, 1.00000, 0.03125, 0.06250, 0.12500, 0.25000, 0.50000, 1.00000, 0.03125, 0.06250, 0.12500, 0.25000, 0.50000, 1.00000, 0.03125, 0.06250, 0.12500, 0.25000, 0.50000, 1.00000, 0.03125, 0.06250, 0.12500, 0.25000, 0.50000, 1.00000)
Response <- c(167.11246201, 53.96960486, 128.42857143, 43.67173252, 4.51975684, 0.34042553, 120.10334347, 101.14589666, 155.17629179, 35.31306991, 8.56534954, 1.71124620, 146.34954407, 108.50151976, 163.60182371, 64.70212766, 2.88145897, 0.50759878, 82.92401216, 109.80547112, 116.69300912, 26.85410334, 3.01519757, 0.37386018, 87.06990881, 84.82978723, 118.36474164, 27.52279635, 2.34650456, 0.10638298, 89.47720365, 109.47112462, 85.43161094, 17.69300912, 2.31306991, 0.07294833)

df <- data.frame(Conc = Conc, Response = Response)


# Make Modell
library(drc)

drm <- drm(Response ~ Conc, data = df, fct = LL2.4())

plot(drm, main = paste("ED(drm, 50):", ED(drm, 50)[[1]]))


# Calculate ED50 (IC50)
ED(drm, 50)