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Thread: No Wald Chi2 or Prob > Chi2 value generated for logistic regression?

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    No Wald Chi2 or Prob > Chi2 value generated for logistic regression?




    I am trying to run a logistic regression analysis using STATA and get the following output:

    Why is no value generated for my Wald Chi2 and Prob > Chi2?
    Am I missing something?

    Background: I am trying to test the odds of using of a particularly innovative diarrhoea treatment kit vs. using the standard from a health center. My outcome is: ORS being prepared in the correct concentration. My predictors are 1) Kit (Kit or HC standard) 2) education of respondent and 3) age group of the respondent.

    Any assistance/advice would be greatly appreciated.


    Code: 
    xi: logistic correct_concentration2 kitvsHC_2wks i.educ_resp i.agegrp_resp if Q7026!=2 & age_resp !=
    > 3 & age_resp !=888 & age_resp !=999 & age_resp !=237 & age_resp !=533, vce (cluster site)
    i.educ_resp       _Ieduc_resp_1-888   (naturally coded; _Ieduc_resp_1 omitted)
    i.agegrp_resp     _Iagegrp_re_1-8     (naturally coded; _Iagegrp_re_1 omitted)
    note: _Ieduc_resp_5 != 0 predicts success perfectly
          _Ieduc_resp_5 dropped and 3 obs not used
     
    note: _Ieduc_resp_888 != 0 predicts success perfectly
          _Ieduc_resp_888 dropped and 1 obs not used
     
     
    Logistic regression                               Number of obs   =        397
                                                      Wald chi2(11)   =          .
                                                      Prob > chi2     =          .
    Log pseudolikelihood = -190.18305                 Pseudo R2       =     0.1670
     
                                                (Std. Err. adjusted for 13 clusters in site)
    ----------------------------------------------------------------------------------------
                           |               Robust
    correct_concentration2 | Odds Ratio   Std. Err.      z    P>|z|     [95% Conf. Interval]
    -----------------------+----------------------------------------------------------------
              kitvsHC_2wks |   11.24157   3.880782     7.01   0.000     5.714488    22.11445
             _Ieduc_resp_2 |   1.157984   .4555998     0.37   0.709     .5355547    2.503809
             _Ieduc_resp_3 |   1.170778   .2816866     0.66   0.512     .7305961    1.876168
             _Ieduc_resp_4 |   2.180526   1.143241     1.49   0.137     .7803323    6.093166
             _Ieduc_resp_5 |          1  (omitted)
             _Ieduc_resp_6 |   1.337406   .5192558     0.75   0.454     .6248549    2.862512
           _Ieduc_resp_888 |          1  (omitted)
             _Iagegrp_re_2 |   1.718779   1.093071     0.85   0.394     .4941875    5.977895
             _Iagegrp_re_3 |   1.337017   .6823091     0.57   0.569     .4917569    3.635162
             _Iagegrp_re_4 |    1.46303   .7253979     0.77   0.443     .5536198    3.866296
             _Iagegrp_re_5 |   .9990781   .5096386    -0.00   0.999     .3676157    2.715219
             _Iagegrp_re_6 |   1.076808   .6089375     0.13   0.896     .3554528    3.262081
             _Iagegrp_re_7 |   1.127842   .4819446     0.28   0.778     .4881083    2.606034
             _Iagegrp_re_8 |   .5456664   .4652697    -0.71   0.477      .102598    2.902121
                     _cons |    .895124   .5374177    -0.18   0.854     .2759535    2.903558
    ----------------------------------------------------------------------------------------
    Last edited by Dason; 06-10-2015 at 10:03 AM.

  2. #2
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    Re: No Wald Chi2 or Prob > Chi2 value generated for logistic regression?

    A quick guess at what is going wrong one variable perfectly predicts ... perhaps then 0 wrong predictions ... then wald statistic cannot be calculated because of division with 0

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    Re: No Wald Chi2 or Prob > Chi2 value generated for logistic regression?

    Quote Originally Posted by JesperHP View Post
    A quick guess at what is going wrong one variable perfectly predicts ... perhaps then 0 wrong predictions ... then wald statistic cannot be calculated because of division with 0
    Thanks very much JesperHP. This is helpful.

    Part of the reason I though that may not be the case was because when I ran the regression with just the Kit vs. Standard ("kitvsHC_2wks") and education of respondent ("educ_resp") predictors it gave me the Chi 2 values, even though the values for "5.educ_resp" and "888.educ_resp" were equal to 0 and predicted success perfectly (see output below). It was only once I added "age_resp" as a predictor that the values were not generated.

    So, in that case, is there a way to just drop those particular levels of the categorial predictor? (i.e. can I drop the "5.educ_resp" and "888.educ_resp") somehow? Any idea of how I would add this to my STATA command?

    I appreciate your help.



    . logistic correct_concentration2 kitvsHC_2wks i.educ_resp if Q7026!=2, vce (cluster site)
    note: 5.educ_resp != 0 predicts success perfectly
    5.educ_resp dropped and 3 obs not used

    note: 888.educ_resp != 0 predicts success perfectly
    888.educ_resp dropped and 1 obs not used


    Logistic regression Number of obs = 399
    Wald chi2(5) = 132.64
    Prob > chi2 = 0.0000
    Log pseudolikelihood = -191.87728 Pseudo R2 = 0.1618

    (Std. Err. adjusted for 13 clusters in site)
    ----------------------------------------------------------------------------------------
    | Robust
    correct_concentration2 | Odds Ratio Std. Err. z P>|z| [95% Conf. Interval]
    -----------------------+----------------------------------------------------------------
    kitvsHC_2wks | 11.4292 3.91619 7.11 0.000 5.839204 22.37063
    |
    educ_resp |
    Grade 5 to 7 | 1.181916 .4321522 0.46 0.648 .5772393 2.420011
    Grade 8 to 9 | 1.209429 .2684513 0.86 0.392 .7827857 1.868605
    Grade 10 to 12 | 2.40131 1.198986 1.75 0.079 .9024831 6.389361
    Higher learning | 1 (empty)
    None | 1.268956 .4702983 0.64 0.520 .6137276 2.62372
    Don't Know | 1 (empty)
    |
    _cons | 1.169003 .3305954 0.55 0.581 .6715755 2.034869
    ----------------------------------------------------------------------------------------

  4. #4
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    Re: No Wald Chi2 or Prob > Chi2 value generated for logistic regression?


    I see youre point ... however this question:
    So, in that case, is there a way to just drop those particular levels of the categorial predictor? (i.e. can I drop the "5.educ_resp" and "888.educ_resp") somehow?
    is about stata - I dont know stata - and in any case you have a better chance of getting help if you pose this question under the the STATA section.

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