[Limdep Nlogit List] Question on missing values in N-logit

David Hensher david.hensher at sydney.edu.au
Wed May 19 18:04:26 AEST 2021


Missing data can exist for  a number of reasons. While not being sure what is happening here there are two codes of value. -999 will remove an entire choice set and -888 will ignore an attribute level associated with an alternative or individual you have in the data. So if a covariant is say income, code as -888 to retain the choice set but note this amounts to it being missing which can be problematic if you too many of these are missing and it is retained in the model. Some people either replace it with the mean or mode or run an auxiliary regression to try and predict it based on other covariates.
David

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On 19 May 2021, at 5:51 pm, Christoph Buschmann <christoph.buschmann at thuenen.de> wrote:

Dear group,

I have a question on how N-logit deals with missing data in the covariates. My choice experi-ments were carried out completely by all respondents, but 8 respondents did not answer all questions about the covariates.

I have ten choice cards per respondent and 3 alternatives in each choice situation. So, my dataset comprises three rows for each choice situation. N-Logit reports that, for the 8 respondents in question, per choice situation one missing value has been found and refers to the first row per choice situation, i.e. the row that gives information about the choice of alternative 1.

I assume that, for the 8 respondents in question, N-logit skips one row per choice situation (the one for alternative 1), including the information about covariates, and keeps the other two rows (for alternatives 2 and 3).

This would mean that for the 8 respondents in question, some of the information is retained and so it makes sense to keep them in the data set. In fact, if I remove the 8 respondents from the dataset by hand, the model deteriorates (AIC).

What is your experience with missing data? Is my interpretation correct?

Thank you very much for your help.


Kind regards,

Christoph Buschmann

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