nested logit about cell phone

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nested logit about cell phone

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I have conducted a pet project about smartwatches and collected some data. I ran a clogit and am trying to do a nested logit model. I haven't done a nlogit before. Thus, I am not sure how to calculate the probabilities of selecting the alternatives at the bottom level and the probabilities of selecting the branches on the top level. If someone could help I would really appreciate it!

First, here is my 2 levels tree structure

Here is my nlogit codes:
nlogit choice <all alternative specific variables> || type: platforminterest, base (none)|| alt:, noconstant case(groupid) nolog

Please note that platforminterest is a case-specific variable with values 1, 2, 3 where 1 means currently using android platform for their cell phone, 2 means using ios platform, 3 means not interested in buying at all.

Below is the output, I do notice that many of the coefficients are not significant. That's because I have less than 20 responses...anyway, let's assume all coefficients are significant for the sake of illustration...

- What are the coefficients in 'type equations' used for?
- How can I calculate the probabilities of 4 alternatives and the probabilities of selecting each branch?

I also asked Stata to predict:
- p1: probabilities of selecting each branch at the top level
- p2: probabilities of selecting each alternative at the bottom level
- condp: conditional probabilities of selecting an alternative given a branch is chosen
- xb1: linear prediction at the top level - same as the type equation coefficients in the output
- xb2: linear prediction at the bottom level
- iv: inclusive value

I know how to calculate xb2. And I know that p2= p1*condp. But I am not sure how to calculate p1 and condp. And what is the role of iv? Any advice would be helpful. Thanks!