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From |
"Rodrigo A. Alfaro" <raalfaroa@gmail.com> |

To |
<statalist@hsphsun2.harvard.edu> |

Subject |
st: nlogit with dummies (follow up) |

Date |
Thu, 26 Jul 2007 17:41:47 -0400 |

Bidisha,

I guess that you have missing SEs because there are too much dummy variables in your model and there are many missing observations on the dataset... right? The latter could be 'solved' by creating imputed datasets (see -ice- or http://www.multiple-imputation.com for more information). About the dummies I don't know if you are technically able to identify the model using mostly dummies. You should check your output and descriptive with someone in your school or give us more info about what happens with your data.

Rodrigo.

PS: Reply to the list, then you could have more feedback from other users.

----- Original Message ----- From: "Bidisha Sayema" <lexshb@nottingham.ac.uk>

To: "Rodrigo A. Alfaro" <raalfaroa@gmail.com>

Sent: Thursday, July 26, 2007 10:36 AM

Subject: RE: st: NLOGIT

Many thanks indeed. I was able to run a nested logit but lot of my

variables came without SE or Z values. I think this is due to the use of

lot of variables (in bottom stage 20 and top stage 25 variables) where

most are dummies and there is no character specific variable. I however

dropped 1 bottom and 1 top category (with all interactions) from my

model but it seems that it was not sufficient. I used interaction of all

individual specific variables with the choices as I thought that is the

procedure to do Nlogit (to interact every variable with choices) and

also thought it would be useful to know about the sign and significance

of those coefficient. It would be appreciated if you could suggest me of

any way to capture the missing SEs.

Regards

Bidisha

*by MNL I meant Multinomial Logit.

-----Original Message-----

From: Rodrigo A. Alfaro [mailto:raalfaroa@gmail.com]

Sent: 26 July 2007 06:51

To: lexshb@nottingham.ac.uk

Subject: Fw: st: NLOGIT

Check that (1) Your Stata is updated. -nlogit- was fixed for missing

observations.

(2) Your covariates are not all dummies. Manos suggested to get some multiplicative variables: something like "married (dummy) times income

(in dollars)". Also, if ageskl is age times dummy-skilled and age times dummy-unskilled why you have both? (3) Drop the nolog in the process... maybe there is some information that we/you want to know, such as "not concave", "variable xyz dropped

due to collinearity", etc. (4) Run a SIMPLE version of the model... I meant really simple. You should play with fraction of your dataset, and less covariates. Rodrigo. ----- Original Message ----- From: "Neil Shephard" <nshephard@gmail.com> To: <statalist@hsphsun2.harvard.edu> Sent: Tuesday, July 24, 2007 8:13 AM Subject: Re: st: NLOGITMNL == Multiple Nested Logit? You've given us the command that you use, but not shown what the error's Stata is reporting are. These are likely to be informative in helping resolve your problem. From the FAQ (http://www.stata.com/support/faqs/res/statalist.html#advice)... * Say exactly what you typed and exactly what Stata typed (or did)

in response. N.B. exactly! If you can, reproduce the error with one of Stata's provided datasets or a simple concocted dataset that you include in your posting. Don't send examples like this, which gives no information: o The command -fiddle- worked yesterday, but it is not working today. or like this, which gives very little information: * I am using -frog-, but I just get the message "invalid

syntax".

This example shows better style, setting aside the fact that its answer can be found in the online help: * I am using Stata 9 to try to draw a plot using -scatter-. Here is an example showing my problem with the auto data: . scatter mpg weight, s(p) I get lots of very small points. Why doesn't Stata use plus symbols? Neil On 7/24/07, Bidisha Sayema <lexshb@nottingham.ac.uk> wrote:Dear Statalisters, I have done a MNL of employment status (4 choices: wage employed, unemployed etc) with individual specific controls eg sex, education,

age, race etc and in the next stage with only the wage employed run another MNL of occupational choices (3 choices: skilled, unskilled etc) with controls like the first stage (not the same though). But I

also want to do a NLOGIT while incorporating all the decisions, so there will be 6 choices in the bottom set (3 choices out of wage employed, 3 remaining categories of employment status) along with the first set of 4 alternatives. I constructed the data set and the tree is running fine but I was unable to run NLOGIT and was facing error message. Is it due to the use of common individual specific variables in both stages? But I need to have demographic and education variables in both stages. Any suggestion is highly appreciated. A simple version of the model is as follows: nlogit choice (occchoice=ageprof ageskl ageuskl agesemp ageunemp agenemp /* */ age2prof age2skl age2uskl age2semp age2unemp age2nemp) (empstat=ageemp2 ageemp3 ageemp4 /* */ age2emp2 age2emp3 age2emp4 marriedemp2 marriedemp3 marriedemp4), group(caseno) nolog Best Regards Bidisha

* * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

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