Dear all,
  I have a question on the four parameter logistic regression.
Not sure about how to set the start values for the parameters.
Can anyone familiar with this give some hint? Thanks so much.


     Hannah



For example, suppose I have the following data values,

> temp
              mean_std
 [1,]     0.0      139
 [2,]     0.5      142
 [3,]     1.0      143
 [4,]     2.0      145
 [5,]     4.0      155
 [6,]     7.0      169
 [7,]    15.0      184
 [8,]    30.0      220
 [9,]    60.0      242
[10,]   150.0      269
[11,]   300.0      283
[12,]   600.0      289
[13,]  1500.0      291
[14,]  3000.0      299
[15,] 10000.0      299


logitfit <- nls(log(mean_std) ~ A+(B-A)/(1+(std[,1]/C)^scal), data=temp,
start=list(A=3.5, B=15, C=600, scale=2.5))
These starting values are not working!

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