Posted by
Maguin, Eugene on
Dec 31, 2012; 4:13pm
URL: http://spssx-discussion.165.s1.nabble.com/Fixed-Effects-Model-LSDV-and-Overfitting-tp5717179p5717181.html
Perhaps 'daze' would be a better word than 'faze'!?
That aside, it seems to me that you have a (very) industrious topic for a senior thesis and that you must have an industrious senior thesis advisor. And, therefore, that person ought to know or know who at your institution knows about analyzing the kind of data that you have. That person is your advisor and they should advise.
That said, please begin by defining 'LSDV'. Others on the list will know more than I do about this type of analysis problem. You have data for 17 time periods for each of 47 states. That data must be arranged in a long format file which will given you 47*17=799 records. In addition to your main IVs, you need to model state differences and time differences, so you have 46 state dummies and 16 time dummies. So your dof will be 799 - 46 - 16 - 4 - 1 = 732. Is your Rsq too high? Hard to tell; it depends on your correlations. What does the correlations of the 4 IVs and the DV look like (ignore the dummies for the moment)?
Gene Maguin
-----Original Message-----
From: SPSSX(r) Discussion [mailto:
[hidden email]] On Behalf Of Molte
Sent: Monday, December 31, 2012 10:11 AM
To:
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Subject: Fixed Effects Model (LSDV) and Overfitting??
Hi,
I am currently in the end faze of writing my bachelor's thesis in political science where I use a panel data set to investigate the effects of corporate contribution bans on policy outcomes on state level. Since I don't have much statistical background to draw upon I've been forced to read up on panel data, how to model it and different problems as I've gone along.
Now I've encountered one problem which I don't know how to tackle and hopefully someone here will be able to offer some advice. My question is if my model is overfitted (a concept I just discovered). I first got suspicious due to the very high value of my models R-squared (0,766) despite the fact that I'm only using 4 predictor variables. The 732 degrees of freedom also appears very high to my untrained eye. Due to my use of LSDV I also have 62 dummy variables (the study includes 47 states and 17 time periods, resulting in 46+16 dummy variables) Could this have resulted in that my model now is too complex and that I should apply a bootstrap or another similar test?
I greatly appreciate all help and wish you all a happy new year.
Best,
A. Severin
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