Hello list,
I'm running -xttobit- models, and getting output that I don't
understand. Below you'll find both my command line and the output.
Scrolling through the output, you'll see that Stata gives me a
coefficient, but no std. err., conf. interval, etc. for the [mxNAFmS_lt]
variable. I've had variables drop out before because of collinearity,
but never gotten a coefficient without the other output. What is even
more odd, is that if I take *ANY* one variable out of the model, I get
full output for all variables. I played around to see if the problem
was with correlations between [mxNAFmS_lt] and some other variable, but
as I say, if I drop *any* one other variable, the model runs fine.
Also, if I change my year dummies (i.e., [close1996]-[close1999]) and
use, say 1997-2000, the model runs fine. And if I remove the -if-
statement in the command, the model runs fine with all the variables.
Anyone have any ideas why I'm getting this partial output in some cases,
but not others??
Thanks,
Tom
.xttobit NALpS_t nLPQFnds nLPFndInv mxNFmInv_lt mxNFmFd_lt LgFmCap
close1996 close1997 close1998 close1999 mxNAFmS_lt if fstlpfminv==1 ,
i(firmid) ll(0) nolog
Random-effects tobit regression Number of obs =
1560
Group variable (i): firmid Number of groups =
103
Random effects u_i ~ Gaussian Obs per group: min =
1
avg =
15.1
max =
100
Wald chi2(9) =
.
Log likelihood = 415.31642 Prob > chi2 =
.
------------------------------------------------------------------------
------
NALpS_t | Coef. Std. Err. z P>|z| [95% Conf.
Interval]
-------------+----------------------------------------------------------
------
nLPQFnds | .1104854 .0031582 34.98 0.000 .1042954
.1166754
nLPFndInv | .0036929 .0098795 0.37 0.709 -.0156707
.0230564
mxNFmInv_lt | .0055975 .0015129 3.70 0.000 .0026322
.0085628
mxNFmFd_lt | .0104735 .0082937 1.26 0.207 -.0057819
.0267288
LgFmCap | .0237823 .0060292 3.94 0.000 .0119653
.0355993
close1996 | .2862993 .0326511 8.77 0.000 .2223043
.3502944
close1997 | -.13454 .0261689 -5.14 0.000 -.1858302
-.0832499
close1998 | -.0424031 .018431 -2.30 0.021 -.0785272
-.006279
close1999 | -.0106964 .0199639 -0.54 0.592 -.049825
.0284323
mxNAFmS_lt | -.1413993 . . . .
.
_cons | -.1813773 .0520966 -3.48 0.000 -.2834848
-.0792699
-------------+----------------------------------------------------------
------
/sigma_u | .1393658 .0073951 18.85 0.000 .1248717
.1538599
/sigma_e | .1737762 .0032071 54.19 0.000 .1674905
.1800619
-------------+----------------------------------------------------------
------
rho | .3914234 .026979 .3396981
.4451459
------------------------------------------------------------------------
------
*****************************************
Thomas P. Moliterno
Graduate School of Management
University of California, Irvine
*****************************************
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