Monday, March 06, 2006

st: xtlogit re versus xtlogit pa

Hi,

My observations are person/years and the dependent variable is whether a person in any given year is registrated as "in continuing education, full-time" (= 1) versus "not" (= 0); that is, still is in regular employment. The independent variables are gender, work experince in years, time (i.e. observation year plus some controls.

My "problem" is that the predicted probabilities from respectively -re- and -pa- differ substantially.

1. Why does the -re- model, for various combinations of the x-values, in general produce lower predicted probabilities than the -pa- model? (By the way, the results for the -pa- model is more in agreement with the plain -logit, cluster (id)- model's results than the -re- model.)

2. Only the -pa- model has a robust option. But why would do I need a robust option in this case? Does not the -xt- option "solve" the issue of many observations for the same person. Or does the robust option solve some other issue in this regard, such as arbitrary serial correlation between panels?

Thanks in advance for any help.

Christer Thrane

************************************************ Professor Christer Thrane Department of Social Science Lillehammer University College 2626 Lillehammer, Norway + 47 61 28 81 70 (fax) + 47 61 28 82 47 (phone, work) + 47 61 25 53 04 (phone, home) E-mail, work: christer.thrane@hil.no E-mail, home: ch-thran@online.no ************************************************

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