st: btscs, cubic splines and predicting meaningful values

["Lukas Kasten" <lukas.kasten@gmx.de>]

Dear all,

i am a student of international relations and I have one short question for 
you:

I am working  with a tscs- structured dataset and I am computing a logit 
modell with  natural cubic splines following Beck, Katz and Tucker (1998) to 
control for time dependency. I used the - btscs- package to generate the 
necessary variables spellcount and _spline*

The command is as usual:

logit depvar idepvar1 idepvar2 ... spellcount _spline1 _spline2 _spline3, 
vce(robust)

I now want to compute perdicted probabilities with  - prvalue - .

My main question is, how to set the values of the variables spellcount and 
spline1 - spline3?  Does it really make sense to set them on their mean? Or 
e.g. should I take the mean duration time until the analysed event occurs 
and set the splines accordingly to that value? (For example if the mean 
duration time is 5, then using - prvalue-  I could set the spellcount on 5 
and set the splines on the values which were computed by - btscs - for a 
duration time of 5.)

Is there any good procedure for setting the splines on meaningful values so 
that you can interpret the perdicted probabilities in a meaningful way?

I already had a look on some publicated articles in which also splines and 
btscs- procedure were used. Most of them set the splines on their means, but 
I am really not sure if that is correct.

I would be very thankful for any tips or hints..
best regards
Lukas 

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