# st: c_logit and dropped observations

 From To Subject st: c_logit and dropped observations Date Sun, 1 Oct 2006 17:56:28 +0100

```Dear Satalist,

I am estimating a conditional logit with the following characteristics:

-Number of decision makers=6,329
-Number of choices=242
-Number of observations=1,531,618 (=6,329*242)
-Decision makers are firms which decide where to locate over a set of 242 location alternatives and independent variables are economic characteristics of the location alternatives.

When estimating the conditional logit I obtain the following message:

"6 groups (1446 obs) dropped due to all positive or all negative outcomes"

clogit choice  n2_gdp n2_gdppc n2_mp n2_w2_2 n2_unemp_r l_n2_managg_s n2_fdi n2_popden, group(id)
note: 6 groups (1446 obs) dropped due to all positive or
all negative outcomes.
Iteration 0:   log likelihood = -31564.979
Iteration 1:   log likelihood = -31562.865
Iteration 2:   log likelihood = -31562.865
Conditional (fixed-effects) logistic regression   Number of obs   =    1529212
LR chi2(8)      =    6279.48
Prob > chi2     =     0.0000
Log likelihood = -31562.865                       Pseudo R2       =     0.0905
------------------------------------------------------------------------------
choice |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
n2_gdp |   .2244931   .0260914     8.60   0.000     .1733548    .2756314
n2_gdppc |  -.3560138    .033739   -10.55   0.000    -.4221411   -.2898865
n2_mp |   .0513986   .0350509     1.47   0.143    -.0172999    .1200972
n2_w2_2 |  -.1733384    .047729    -3.63   0.000    -.2668855   -.0797913
n2_unemp_r |  -.0770995   .0209851    -3.67   0.000    -.1182295   -.0359696
l_n2_manag~s |   .0490496   .0404983     1.21   0.226    -.0303257    .1284248
n2_fdi |   .9064167   .0160668    56.42   0.000     .8749263     .937907
n2_popden |   .4422606   .0792087     5.58   0.000     .2870145    .5975067
------------------------------------------------------------------------------

As far as I know this means that within those 6 groups (in my case firms) all observations have the same value for the dependent variable.

However I have made several checks and I have one 1 for each group and the rest zeros and also have checked that there are 242 choices for each group.

1/ Can anyone tell me why I am still having this problem?

2/ Is there any way to say stata to tell me which are the 6 groups which are being dropped?

3/ If 6 groups are being dropped, then 6*242=1,452 observations should be dropped but in the message above the observations dropped are 1,446. Why?

I appreciate any comment or help,

Thanks!,

---Rodrigo

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