Probit - omitted variables

Hi all,

I am currently encountering difficulties concering a probit analysis.

I am researching the factors that influence a company's decision to withdraw. So my dependent variable is withdrawn, equaling 1 if an offer is withdrawn, zero otherwise.

Now I am trying to run a probit on roughly 20 variables.


. tab withdrawn

Withdrawn | Freq. Percent Cum.
------------+-----------------------------------
completed | 5,644 72.81 72.81
withdrawn | 2,108 27.19 100.00
------------+-----------------------------------
Total | 7,752 100.00

I ran the following Regression as an example with the follwoing results:
. probit withdrawn log_filing_size ff_tech_dummy age vc_dummy numberofbookrunners

Probit regression Number of obs = 1323
LR chi2(5) = 299.51
Prob > chi2 = 0.0000
Log likelihood = -168.45198 Pseudo R2 = 0.4706

-------------------------------------------------------------------------------------
withdrawn | Coef. Std. Err. z P>|z| [95% Conf. Interval]
--------------------+----------------------------------------------------------------
log_filing_size | -.4581109 .0412589 -11.10 0.000 -.5389768 -.377245
ff_tech_dummy | -.225391 .2643792 -0.85 0.394 -.7435647 .2927826
age | -.0174898 .0078032 -2.24 0.025 -.0327838 -.0021958
vc_dummy | -.9559697 .2673385 -3.58 0.000 -1.479943 -.431996
numberofbookrunners | .3216903 .4369625 0.74 0.462 -.5347405 1.178121
_cons | -.2143128 .4574461 -0.47 0.639 -1.110891 .682265
-------------------------------------------------------------------------------------

However, if I run it with one more variable included, the results for vc_dummy are omitted:
probit withdrawn log_filing_size ff_tech_dummy age vc_dummy numberofbookrunners uw_ranking


note: vc_dummy != 0 predicts failure perfectly
vc_dummy dropped and 333 obs not used

Probit regression Number of obs = 490
LR chi2(5) = 2.17
Prob > chi2 = 0.8252
Log likelihood = -55.281123 Pseudo R2 = 0.0192

-------------------------------------------------------------------------------------
withdrawn | Coef. Std. Err. z P>|z| [95% Conf. Interval]
--------------------+----------------------------------------------------------------
log_filing_size | .06986 .1482238 0.47 0.637 -.2206532 .3603733
ff_tech_dummy | -.129397 .4416797 -0.29 0.770 -.9950733 .7362794
age | -.0087463 .0086231 -1.01 0.310 -.0256472 .0081546
vc_dummy | 0 (omitted)
numberofbookrunners | .295596 .3318717 0.89 0.373 -.3548605 .9460524
uw_ranking | -.0446172 .0654074 -0.68 0.495 -.1728133 .0835789
_cons | -2.120634 .5625254 -3.77 0.000 -3.223163 -1.018104
-------------------------------------------------------------------------------------

tab vc_dummy

VC-backed | Freq. Percent Cum.
------------+-----------------------------------
0 | 3,666 61.60 61.60
1 | 2,285 38.40 100.00
------------+-----------------------------------
Total | 5,951 100.00



If I include all the variables I want to run the regression on, I get the following message and no output is created:

note: vc_dummy != 0 predicts failure perfectly
vc_dummy dropped and 76 obs not used

note: numberofbookrunners != 1 predicts failure perfectly
numberofbookrunners dropped and 1 obs not used

note: no_industry_filings != 56 predicts failure perfectly
no_industry_filings dropped and 42 obs not used

outcome = age <= 1 predicts data perfectly

I don't really understand why the vc_dummy is omitted in the 2nd regression while it is included in the first one.
Also I don't know why I don't get results for the Regression on all the variables.

I would really apreciate any help.