st: Cragg-Donald Statistic in ivreg2

 From Justin Smith To statalist@hsphsun2.harvard.edu Subject st: Cragg-Donald Statistic in ivreg2 Date Sun, 11 Jun 2006 18:43:31 -0400

```I am trying to calculate some statistics for weak instruments in Stata,
and some of the previous statalist questions seem to indicate that
ivreg2 combined with the "ffirst" option will report the Cragg-Donald
statistic.

When I type the following (variable names are unimportant):

ivreg2 sperce  rbd11 -  rbd15 (age xrep xstartlate = c2-c5), ffirst

it gives the following output...

First-stage regressions
-----------------------

Summary results for first-stage regressions:

Shea
Variable      Partial R2      Partial R2       F(  4,196341)    P-value
age             0.0024          0.6450          89191.70         0.0000
xrep            0.0001          0.0090            444.08         0.0000
xstartlate      0.0000          0.0302           1528.72         0.0000

Instrumental variables (2SLS) regression
----------------------------------------

Number of obs =
196351
F(  8,196342) =
213.66
Prob > F      =
0.0000
Total (centered) SS     =  192791.2461                Centered R2   =
-0.0363
Total (uncentered) SS   =  192793.6585                Uncentered R2 =
-0.0363
Residual SS             =  199790.6129                Root MSE      =
1

------------------------------------------------------------------------------
sperce |      Coef.   Std. Err.      z    P>|z|     [95% Conf.
Interval]
-------------+----------------------------------------------------------------
age |   .1938617   .1800731     1.08   0.282     -.159075
.5467984
xrep |  -1.434245   2.340419    -0.61   0.540    -6.021383
3.152893
xstartlate |  -1.292564   2.913459    -0.44   0.657    -7.002838
4.41771
rbd11 |  -.0002252   .0007117    -0.32   0.752    -.0016201
.0011697
rbd12 |   1.03e-06   2.68e-06     0.38   0.701    -4.23e-06
6.29e-06
rbd13 |  -1.70e-09   4.00e-09    -0.43   0.671    -9.53e-09
6.13e-09
rbd14 |   1.15e-12   2.57e-12     0.45   0.655    -3.88e-12
6.18e-12
rbd15 |  -2.75e-16   5.94e-16    -0.46   0.644    -1.44e-15
8.90e-16
_cons |  -1.854898   1.857435    -1.00   0.318    -5.495405
1.785608
------------------------------------------------------------------------------
Sargan statistic (overidentification test of all instruments):
1.102
Chi-sq(1) P-val =
0.29386
------------------------------------------------------------------------------
Instrumented:  age xrep xstartlate
Instruments:   c2 c3 c4 c5 rbd11 rbd12 rbd13 rbd14 rbd15
------------------------------------------------------------------------------

I expected to see the underidentification diagnostics, but they do not
appear.  Is there and update I need for ivreg2 that will give this
information?

Thank you,

Justin Smith
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```