Hints & Tips on DEBtox
Page updated on 11 Februari 1996
Here are some questions and and answers about using DEBtox in practice.
- I often encounter runtime errors especially when running the profile
likelihood procedure to determine the confidence parameters.
We also have encountered this problem once or twice. Numerical procedures,
especially with the reproduction experiment, are quite complex. We are
still working on them to ameliorate them. Could you send me a dataset that
caused a run-time error??
- The fitted parameters are highly correlated, sometimes reaching
correlation coefficient equal to 1. From my experience with regression
this is not acceptable and lead to errors in parameters.
This is mostly the case when the resulting NEC is very small (practically
zero), together with a very small elimination rate and very small tolerance
concentration. I should expect the procedure to choose for the limit case
where the elimination rate is zero.
- The NEC value is sometimes very close to 0 in contradiction with
the corresponding concentration profile.
The NEC is the no-effect concentration after infinite exposure. In
the concentration profile you see the no-effect concentration after seven
days. Especially when the elimination rate is very small, differences can
be large. In these cases you will probably find broad confidence intervals.
- Do you know the right growth parameters for Ceriodaphnia dubia?
I used the same size that you use for Daphnia magna since it is scaled
and both animals get the same shape. I found 0.15 to fit well as a von
Bertalanffy growth rate after some trials with different values.
We don't know the growth parameters for Ceriodaphnia dubia. But I saw
a different solution. Is it possible that you didn't start with neonates?
I got a equally good fit with a growth parameter at the value 0.10 and
a initial length value of 0.25.
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