Latent Class Example: Why setting B_TIME_RND[0] = 0？

[Jianing Liu]

Dear Professor Birelaire, 

Hope this post finds you well.

I'm a beginner of biogeme and I'm working on a latent class model with the reference to the "15panelDiscrete" example. I was wondering why we should set B_TIME_RND[0] = 0?

More specifically, my current understanding is that only by normalizing one of the parameters of one of the classes to zero could the classes be deffientiated from each other, am I on the right track? If so, how should I interprete the results of B_TIME? (Since intuitively both classes should have some sentivity to travel time. )

Moreover, should we always set one of the classes of one of the latent paramters to zero? And if so, is there any criteria to select which parameter to be fixed? For example in "15panelDiscrete", why we set B_TIME_RND[0] = 0 instead of ASC_CAR_RND[0] = 0 ?

Sorry to bother you with these beginner questions. I would be very grateful if you can give some advise.

Best

Jianing

[Bierlaire Michel]

On 16 Oct 2021, at 17:11, Jianing Liu <ichf...@gmail.com> wrote:

Dear Professor Birelaire, 

Hope this post finds you well.

I'm a beginner of biogeme and I'm working on a latent class model with the reference to the "15panelDiscrete" example. I was wondering why we should set B_TIME_RND[0] = 0?

It is simply the assumption of the model. We assume that individuals in class 0 did not play the SP game correctly, and ignored the time coefficient. This is an example that I took from one of my lectures. And I realize that this is to properly documented in the file itself. 

https://youtu.be/9YzqmpjZTjQ

More specifically, my current understanding is that only by normalizing one of the parameters of one of the classes to zero could the classes be deffientiated from each other, am I on the right track? If so, how should I interprete the results of B_TIME? (Since intuitively both classes should have some sentivity to travel time. )

Moreover, should we always set one of the classes of one of the latent paramters to zero?

No. You should specify a model in a latent class exactly the same way as you would specify it with the class was observed, characterized by socio-economic characteristics. 

And if so, is there any criteria to select which parameter to be fixed? For example in "15panelDiscrete", why we set B_TIME_RND[0] = 0 instead of ASC_CAR_RND[0] = 0 ?

Again, setting beta_time to zero is very specific to this example. It is associated with a specific behavioral assumption, and not with a structural property of the model.

Sorry to bother you with these beginner questions. I would be very grateful if you can give some advise.

Best

Jianing

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[Jianing Liu]

Dear Professor Birelaire, 

Thanks so much for your detailed explanation!

Best,

Jianing