Important: Read this before posting to this forum

  1. This forum is for questions related to the use of Apollo. We will answer some general choice modelling questions too, where appropriate, and time permitting. We cannot answer questions about how to estimate choice models with other software packages.
  2. There is a very detailed manual for Apollo available at http://www.ApolloChoiceModelling.com/manual.html. This contains detailed descriptions of the various Apollo functions, and numerous examples are available at http://www.ApolloChoiceModelling.com/examples.html. In addition, help files are available for all functions, using e.g. ?apollo_mnl
  3. Before asking a question on the forum, users are kindly requested to follow these steps:
    1. Check that the same issue has not already been addressed in the forum - there is a search tool.
    2. Ensure that the correct syntax has been used. For any function, detailed instructions are available directly in Apollo, e.g. by using ?apollo_mnl for apollo_mnl
    3. Check the frequently asked questions section on the Apollo website, which discusses some common issues/failures. Please see http://www.apollochoicemodelling.com/faq.html
    4. Make sure that R is using the latest official release of Apollo.
  4. If the above steps do not resolve the issue, then users should follow these steps when posting a question:
    1. provide full details on the issue, including the entire code and output, including any error messages
    2. posts will not immediately appear on the forum, but will be checked by a moderator first. This may take a day or two at busy times. There is no need to submit the post multiple times.

Joint model of two discrete choices

Ask questions about model specifications. Ideally include a mathematical explanation of your proposed model.
Post Reply
samesag
Posts: 4
Joined: 28 Jan 2021, 15:56

Joint model of two discrete choices

Post by samesag »

Dear David and Stephane,

Thank you for your marvelous work with Apollo.

I'm interested in estimating a joint model for ownership and use preference of motorcycle, using latent variables. I have a dataset from a survey where each responder answer the number of motorcycles owned and the frequency of use. I would like to make a binomial model for ownership (0 = none, 1 = own at least one motorcycle), and a MNL for use preference (where the dependent variable takes the value of 1, if the individual uses the motorcycle less days than the days he/she commutes; 2, if both numbers are equal; and 3, if the individual uses the motorcycle more days than the days he/she commutes.

It would be expected that both decisions are related, as an individual may value the number of days he/she would use the vehicle vs. the days of commuting, and then decide to acquire the motorcycle. Hence, the interest to model both decisions in a joint model. I want to ask you if defining both models (binomial and MNL), and then using the function apollo_combineModels would be enough to "join" both decisions, or if it would be necessary to develop further steps to achieve this using Apollo.

Thank you in advance,

Santiago Mesa
stephanehess
Site Admin
Posts: 974
Joined: 24 Apr 2020, 16:29

Re: Joint model of two discrete choices

Post by stephanehess »

Santiago

using apollo_combineModels will mean that both models contribute to the likelihood of the model. But the actual link between the two requires some parameters to be shared. If both models use completely separate sets of parameters, then the joint LL is simply the sum of the the LLs for two separate models

Stephane
--------------------------------
Stephane Hess
www.stephanehess.me.uk
samesag
Posts: 4
Joined: 28 Jan 2021, 15:56

Re: Joint model of two discrete choices

Post by samesag »

Stephan, thank you for your answer.

May I ask if the parameters to be shared must be the betas of the regression, or there is another way to join both decisions (like using a random coefficient or a latent variable) while keeping independent/separate betas for every choice (ownership, preference of use 1, and preference of use 3).

Santiago
stephanehess
Site Admin
Posts: 974
Joined: 24 Apr 2020, 16:29

Re: Joint model of two discrete choices

Post by stephanehess »

Santiago

if you include a random coefficient, that would still use parameters too, same for a latent variable.

Stephane
--------------------------------
Stephane Hess
www.stephanehess.me.uk
Post Reply