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RE: st: RE: ivprobit is adding extra instruments


From   "Wooldridge, Jeffrey" <[email protected]>
To   <[email protected]>
Subject   RE: st: RE: ivprobit is adding extra instruments
Date   Wed, 9 Mar 2011 10:39:04 -0500

This test always has one df, as it is simply a test of whether the errors in the structural and reduced form equation are correlated.

Jeff

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Sarah Alkenbrack
Sent: Wednesday, March 09, 2011 10:34 AM
To: [email protected]
Subject: Re: st: RE: ivprobit is adding extra instruments

Thank you Mark. Is it a problem that my wald test is showing only 1
df? i.e. Wald test of exogeneity (/athrho = 0): chi2(1) =    73.44
Prob > chi2 = 0.0000

Sarah

On Wed, Mar 9, 2011 at 10:28 AM, Schaffer, Mark E <[email protected]> wrote:
> Sarah,
>
> It's not a "problem" at all.  In econometrics, the term "instrument" is often used to designate an exogenous variable, whether it is included as a regressor or not.
>
> --Mark
>
>> -----Original Message-----
>> From: [email protected]
>> [mailto:[email protected]] On Behalf Of
>> Sarah Alkenbrack
>> Sent: Wednesday, March 09, 2011 3:21 PM
>> To: [email protected]
>> Subject: st: ivprobit is adding extra instruments
>>
>> Hi Stata users,
>>
>> I am running -ivprobit- to look at the determinants of enrolment in
>> health insurance (cbhi). I have several exogenous regressors and one
>> endogenous regressor (consumption).
>> I am using wealthindex as an intrumental variable for consumption.
>> However, when I run the ivprobit model all my exogenous regressors
>> appear in the "instruments" list. Could someone please
>> tell me how to prevent this from happening? I am copying the stata
>> code and results below. I noticed in the archives that others have had
>> this problem but so far, I have not seen any answers
>> posted on what might be causing this problem or how to correct it.
>>
>> Thank you in advance for your help.
>>
>> Sarah
>>
>> . # delimit;
>> delimiter now ;
>> . ivprobit cbhi age_hhead age2 edu_hh2 edu_hh3 edu_hh4 edu_hh5 mar_hh
>> hhmem_cat2 hhmem_cat3
>> > hhhealth_poor hh_chronic hh_diffic risk pregnancy wra
>> any_oldmem j_hh2 j_hh3 j_hh4
>> > hlthseek_mod campaign qual_percep urban door_to_door chief_mem
>> > pharm_in_vil drugsel_in_vil hlthcent_in_vil privclin_in_vil
>> young edu_chief num_camp_vill home_collection
>> > qual2 qual3 size_ln name_hosp1 name_hosp3 name_hosp4
>> name_hosp5 name_hosp6 (cons_pcm=wealthindex) ;
>>
>> Fitting exogenous probit model
>>
>> Iteration 0:   log likelihood = -1909.5425
>> Iteration 1:   log likelihood =  -1687.946
>> Iteration 2:   log likelihood = -1681.6413
>> Iteration 3:   log likelihood = -1681.6142
>> Iteration 4:   log likelihood = -1681.6142
>>
>> Fitting full model
>>
>> Iteration 0:   log likelihood = -42769.776
>> Iteration 1:   log likelihood = -42766.676
>> Iteration 2:   log likelihood = -42736.028
>> Iteration 3:   log likelihood = -42734.629
>> Iteration 4:   log likelihood = -42734.269
>> Iteration 5:   log likelihood = -42734.266
>> Iteration 6:   log likelihood = -42734.266
>>
>> Probit model with endogenous regressors           Number of
>> obs   =       3000
>>
>>                     Wald chi2(42)   =    1113.82
>> Log likelihood = -42734.266                       Prob > chi2
>>     =     0.0000
>>
>> --------------------------------------------------------------
>> ----------------
>>              |      Coef.   Std. Err.      z    P>|z|
>> [95% Conf. Interval]
>> -------------+------------------------------------------------
>> ----------------
>>     cons_pcm |   3.59e-06   2.15e-07    16.68   0.000
>> 3.17e-06    4.01e-06
>>    age_hhead |   .0320042   .0129973     2.46   0.014
>> .00653    .0574784
>>         age2 |  -.0001774   .0001228    -1.45   0.148
>> -.0004181    .0000632
>>      edu_hh2 |    .051426   .0879334     0.58   0.559
>> -.1209203    .2237723
>>      edu_hh3 |  -.0075595   .1023748    -0.07   0.941
>> -.2082106    .1930915
>>      edu_hh4 |   -.000683   .1285689    -0.01   0.996
>> -.2526735    .2513075
>>      edu_hh5 |  -.2986249   .1713749    -1.74   0.081
>> -.6345136    .0372638
>>       mar_hh |  -.0539035    .067056    -0.80   0.421
>> -.1853308    .0775237
>>   hhmem_cat2 |   .4222092   .0675468     6.25   0.000
>> .2898198    .5545985
>>   hhmem_cat3 |   .7099401   .0822271     8.63   0.000
>> .5487778    .8711023
>> hhhealth_p~r |   .1550617   .0699122     2.22   0.027
>> .0180362    .2920872
>>   hh_chronic |    .159681   .0718297     2.22   0.026
>> .0188973    .3004647
>>    hh_diffic |   .2613713   .0741209     3.53   0.000
>> .116097    .4066456
>>         risk |  -.0482252   .0467953    -1.03   0.303
>> -.1399423    .0434919
>>    pregnancy |   .1200344   .1214774     0.99   0.323
>> -.1180569    .3581257
>>          wra |   .1033809   .0289192     3.57   0.000
>> .0467004    .1600614
>>   any_oldmem |   .0792428   .0680778     1.16   0.244
>> -.0541872    .2126729
>>        j_hh2 |   .0512404   .0815692     0.63   0.530
>> -.1086323     .211113
>>        j_hh3 |   -.349126   .0806268    -4.33   0.000
>> -.5071516   -.1911004
>>        j_hh4 |   .1928496   .0843208     2.29   0.022
>> .0275838    .3581154
>> hlthseek_mod |  -.0359996   .0969011    -0.37   0.710
>> -.2259223     .153923
>>     campaign |   .5068671   .0781293     6.49   0.000
>> .3537365    .6599977
>>  qual_percep |   .1840314   .0514758     3.58   0.000
>> .0831408    .2849221
>>        urban |  -.0999875   .0590944    -1.69   0.091
>> -.2158103    .0158353
>> door_to_door |   .0564977   .0719369     0.79   0.432
>> -.084496    .1974914
>>    chief_mem |   .0811248   .0599964     1.35   0.176
>> -.036466    .1987156
>> pharm_in_vil |   .0269211   .0582651     0.46   0.644
>> -.0872763    .1411185
>> drugsel_in~l |   .0693485   .0586169     1.18   0.237
>> -.0455385    .1842355
>> hlthcent_i~l |   .0089279   .0823509     0.11   0.914
>> -.1524769    .1703327
>> privclin_i~l |  -.0547559   .0857815    -0.64   0.523
>> -.2228846    .1133728
>>        young |   .0899074   .0715818     1.26   0.209
>> -.0503903    .2302051
>>    edu_chief |  -.0888131   .0528856    -1.68   0.093
>> -.1924671    .0148408
>> num_camp_v~l |   .0655667   .0548026     1.20   0.232
>> -.0418444    .1729779
>> home_colle~n |   .1944581   .0606159     3.21   0.001
>> .0756531    .3132631
>>        qual2 |  -.1778623   .0896638    -1.98   0.047
>> -.3536001   -.0021245
>>        qual3 |  -.2049839   .1081036    -1.90   0.058
>> -.416863    .0068952
>>      size_ln |  -.0059746    .042326    -0.14   0.888
>> -.0889321    .0769829
>>   name_hosp1 |   .1476783   .1168295     1.26   0.206
>> -.0813032    .3766598
>>   name_hosp3 |    .536909   .1350044     3.98   0.000
>> .2723053    .8015128
>>   name_hosp4 |   .4347936   .1069197     4.07   0.000
>> .2252348    .6443523
>>   name_hosp5 |    .228802   .1274495     1.80   0.073
>> -.0209945    .4785985
>>   name_hosp6 |   .9189969   .1301651     7.06   0.000
>> .6638779    1.174116
>>        _cons |   -4.82205   .4438201   -10.86   0.000
>> -5.691922   -3.952179
>> -------------+------------------------------------------------
>> ----------------
>>      /athrho |  -.8556093   .0998439    -8.57   0.000
>> -1.0513   -.6599188
>>     /lnsigma |   12.27712     .01291   950.98   0.000
>> 12.25181    12.30242
>> -------------+------------------------------------------------
>> ----------------
>>          rho |  -.6939885   .0517571
>> -.7823111   -.5783094
>>        sigma |   214725.5   2772.097
>> 209360.5    220228.1
>> --------------------------------------------------------------
>> ----------------
>> Instrumented:  cons_pcm
>> Instruments:   age_hhead age2 edu_hh2 edu_hh3 edu_hh4 edu_hh5 mar_hh
>>                hhmem_cat2 hhmem_cat3 hhhealth_poor hh_chronic
>> hh_diffic risk
>>                pregnancy wra any_oldmem j_hh2 j_hh3 j_hh4 hlthseek_mod
>>                campaign qual_percep urban door_to_door chief_mem
>>                pharm_in_vil drugsel_in_vil hlthcent_in_vil
>> privclin_in_vil
>>                young edu_chief num_camp_vill home_collection
>> qual2 qual3
>>                size_ln name_hosp1 name_hosp3 name_hosp4 name_hosp5
>>                name_hosp6 wealthindex
>> --------------------------------------------------------------
>> ----------------
>> Wald test of exogeneity (/athrho = 0): chi2(1) =    73.44
>> Prob > chi2 = 0.0000
>>
>> *
>> *   For searches and help try:
>> *   http://www.stata.com/help.cgi?search
>> *   http://www.stata.com/support/statalist/faq
>> *   http://www.ats.ucla.edu/stat/stata/
>>
>
>
> --
> Heriot-Watt University is a Scottish charity
> registered under charity number SC000278.
>
>
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>

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