Hi,
I am using the following dataset and fitting a 4 parameter logistical curve
using drm. However, there is no p value returned for any of the fitted
coefficients and a warning message of NaNs produced is returned. I tried using
both LL.4 and LL2.4. What does the warning message imply? The data fitted here
does not quite match up with the results of Masterplex software. What may I be
doing wrong? Please help.
Weights <-1/(y1^2)
list(all)
[[1]]
x1 y1
1 1500.00 439908
2 1500.00 464838
3 1500.00 467593
4 150.00 26126
5 150.00 26639
6 150.00 26524
7 25.00 3482
8 25.00 3555
9 25.00 3438
10 5.00 790
11 5.00 826
12 5.00 805
13 2.00 443
14 2.00 464
15 2.00 469
16 1.00 337
17 1.00 355
18 1.00 364
19 0.50 278
20 0.50 279
21 0.50 307
22 0.25 241
23 0.25 266
24 0.25 276
FourPL.fit <- drm(y1~x1,weights=weights,data=all,fct=LL2.4())
summary(FourPL.fit <- drm(y1~x1,weights=weights,data=all,fct=LL2.4()))
Model fitted: Log-logistic (log(ED50) as parameter) (4 parms)
Parameter estimates:
Estimate Std. Error t-value p-value
b:(Intercept) -1.144871 0.068434 -16.729579 0
c:(Intercept) 241.482714 7.112223 33.953199 0
d:(Intercept) 423431.818035 NA NA NA
e:(Intercept) 7.319215 NA NA NA
Residual standard error:
0.0001265872 (20 degrees of freedom)
Warning message:
In sqrt(diag(varMat)) : NaNs produced
> summary(FourPL.fit.1 <- drm(y1~x1,weights=weights,data=all,fct=LL.4()))
Model fitted: Log-logistic (ED50 as parameter) (4 parms)
Parameter estimates:
Estimate Std. Error t-value p-value
b:(Intercept) -1.20654 0.07606 -15.86309 0.0000
c:(Intercept) -226.35200 128.30261 -1.76420 0.0930
d:(Intercept) 468060.34801 NA NA NA
e:(Intercept) 292.10119 132.92109 2.19755 0.0399
Residual standard error:
0.003207409 (20 degrees of freedom)
Warning message:
In sqrt(diag(varMat)) : NaNs produced
Master Plex summary:
Initial Top 462020.7967
Initial Bottom 234.9
Initial MidPoint 784.0181741
Initial HillSlope 1
Weighting 1/y^2
Max Iteration 500
Thanks,
Abhi
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