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  • Logit convergence troubles after removing outliers: how to evaluate outliers?

    Dear all,

    In my thesis, I run a logit model on imputed data followed by a prediction of robust standard errors in order to detect outliers in all of my M=10 datasets. Outliers are defined as rsta > 3. I wanted to check whether my results changed when these outliers were removed (just as a sensitivity test, as it is not recommended to remove outliers). However, these models encounter convergence troubles with multiple variables predicting failure/success perfectly. This results in a drastic reduction of observations (2700 to ca. 800).

    My code is as following:
    Code:
    mi xeq: logit violent_success lagfpe lagpolyarchy lnlaggdp lnlagpop lnlagmilper oceania asia europe americas coldwar, vce(cluster country_name); predict rsta, rsta; drop if rsta > 3; logit violent_success lagfpe lagpolyarchy lnlaggdp lnlagpop lnlagmilper oceania asia europe americas, vce(cluster country_name);
    The results from one of the imputed datasets produce the following:

    Code:
    Logistic regression                                     Number of obs =    842
                                                            Wald chi2(0)  =      .
                                                            Prob > chi2   =      .
    Log pseudolikelihood = 0                                Pseudo R2     = 1.0000
    
                                 (Std. err. adjusted for 51 clusters in country_name)
    ---------------------------------------------------------------------------------
                    |               Robust
    violent_success | Coefficient  std. err.      z    P>|z|     [95% conf. interval]
    ----------------+----------------------------------------------------------------
             fpe |  -4363.704          .        .       .            .          
      polyarchy |   7930.141          .        .       .            .           .
             gdp |  -322.5747          .        .       .            .           .
             pop |  -1940.156          .        .       .            .           .
         milper |     47.987          .        .       .            .           .
      oceania |   5060.001          .        .       .            .           .
               asia |          0  (omitted)
             europe |          0  (omitted)
           americas |   9373.118          .        .       .            .           .
            coldwar |   -1260.82          .        .       .            .           .
              _cons |   24333.16          .        .       .            .           .
    ---------------------------------------------------------------------------------
    Note: 834 failures and 8 successes completely determined.
    It would be great to get some advice on how I can evaluate the effects of outliers in my model in any other way than this! I already tried the firthlogit to handle complete separation better, but this does not support clustered standard errors, which I, unfortunately, need to include.
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