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Re: st: -xtpcse and period dummies- no full table reported due to asymmetric and singular variance matrix


From   Felix Wädlich <[email protected]>
To   [email protected]
Subject   Re: st: -xtpcse and period dummies- no full table reported due to asymmetric and singular variance matrix
Date   Mon, 14 Mar 2011 14:13:39 +0100

Hey Justina,

I include gdp as a measure of market size and gdppc as an indicator
for development or wealth.

I tried to build up the covariates, but the problem remains: as soon
as I include the year dummies (yr*), I get the breakdown message. It
probably is a very basic problem, but I just dont see what I am doing
wrong, and also what else I can do. Any more thoughts?

Best,
Felix

2011/3/14 Justina Fischer <[email protected]>
>
> Hi
>
> try to build up the covariates step-by-step and observe when breakdown occurs.
>
> Why do you include gdppc and gdp simulatenously ?
>
> Justina
> -------- Original-Nachricht --------
> > Datum: Mon, 14 Mar 2011 13:39:28 +0100
> > Von: "Felix Wädlich" <[email protected]>
> > An: [email protected]
> > Betreff: Re: st: -xtpcse and period dummies- no full table reported due to asymmetric and singular variance matrix
>
> > Dear Clive,
> >
> > thanks for ur suggestion, but unfortunately that did not do the job.
> > Still getting the same warning message.Any other tip?
> >
> > Best,
> > Felix
> >
> > . xtpcse  c_capital c_loggdppc c_loggdp c_lgovcon c_lgrowth
> > c_lregionothers yr*, pairwise c(ar1)
> >
> > Number of gaps in sample:  8
> > (note: computations for rho restarted at each gap)
> > note: yr1 omitted because of collinearity
> > note: yr2 omitted because of collinearity
> > (note: estimates of rho outside [-1,1] bounded to be in the range [-1,1])
> > (note: at least one disturbance covariance assumed 0, no common time
> > periods
> >       between panels)
> > Warning:  variance matrix is nonsymmetric or highly singular
> >
> > Prais-Winsten regression, correlated panels corrected standard errors
> > (PCSEs)
> >
> > Group variable:   Country                       Number of obs
> >      =      2814
> > Time variable:    year                          Number of
> > groups   =       134
> > Panels:           correlated (unbalanced)       Obs per group: min
> > =         2
> > Autocorrelation:  common AR(1)
> >     avg =        21
> > Sigma computed by pairwise selection
> >   max =        25
> > Estimated covariances      =      9045          R-squared
> >      =    0.0493
> > Estimated autocorrelations =         1          Wald chi2(0)
> >     =         .
> > Estimated coefficients     =        30          Prob > chi2
> >      =         .
> >
> > ------------------------------------------------------------------------------
> >             |           Panel-corrected
> >   c_capital |      Coef.   Std. Err.      z    P>|z|     [95%
> > Conf. Interval]
> > -------------+----------------------------------------------------------------
> >  c_loggdppc |  -.5241978          .        .       .
> >        .           .
> >    c_loggdp |    .110086          .        .       .
> >        .           .
> >   c_lgovcon |   .0016855          .        .       .
> >        .           .
> >   c_lgrowth |   .0008101          .        .       .
> >        .           .
> > c_lregiono~s |   .1941566          .        .       .
> >        .           .
> >         yr1 |  (omitted)
> >         yr2 |  (omitted)
> >         yr3 |    .022493          .        .       .
> >          .           .
> >         yr4 |   .0273882          .        .       .
> >          .           .
> >         yr5 |   .0115461          .        .       .
> >          .           .
> >         yr6 |   .0337352          .        .       .
> >          .           .
> >         yr7 |   .0598745          .        .       .
> >          .           .
> >         yr8 |   .0291169          .        .       .
> >          .           .
> >         yr9 |   .0211556          .        .       .
> >          .           .
> >        yr10 |   .0255307          .        .       .
> >          .           .
> >        yr11 |   .0242099          .        .       .
> >          .           .
> >        yr12 |   .0043918          .        .       .
> >          .           .
> >        yr13 |  -.0247601          .        .       .
> >          .           .
> >        yr14 |   .0009665          .        .       .
> >          .           .
> >        yr15 |   .1060365          .        .       .
> >          .           .
> >        yr16 |   .0805885          .        .       .
> >          .           .
> >        yr17 |   .0332214          .        .       .
> >          .           .
> >        yr18 |   .0832608          .        .       .
> >          .           .
> >        yr19 |   .0403092          .        .       .
> >          .           .
> >        yr20 |   .0195583          .        .       .
> >          .           .
> >        yr21 |   .0004272          .        .       .
> >          .           .
> >        yr22 |    .013192          .        .       .
> >          .           .
> >        yr23 |   .0135001          .        .       .
> >          .           .
> >        yr24 |   .0059468          .        .       .
> >          .           .
> >        yr25 |   .0014196          .        .       .
> >          .           .
> >        yr26 |    -.00606          .        .       .
> >          .           .
> >       _cons |  -.0334178          .        .       .
> >        .           .
> > -------------+----------------------------------------------------------------
> >         rho |   .8822325
> > ------------------------------------------------------------------------------
> >
> >
> > 2011/3/13 Clive Nicholas <[email protected]>:
> > > Felix Waedlich:
> > >
> > >> I have to run a Prais-Winsten-regression with Period-Dummies and
> > panel-corrected standard errors [by xtpcse, corr(ar1)], since my (unbalanced)
> > panel needs correction for serial correlation, groupwise heteroskedasticity
> > and contemporaneous correlation. I need the period dummies to control for
> > common shocks and trends, since I have a Diffusion variable respectively
> > spatial lag, which requires a conservative test against alternative external
> > influences.
> > >> Without period dummies, there appears to be no problem: Stata reports
> > me all the coefficients, the z-values, etc. But when I include the period
> > dummies, Stata says "warning: variance matrix is nonsymmetric or highly
> > singular", and only lists the coefficients, but no standard errors, no z-values,
> > etc.. Since this is a standard specification in my field of research, I am
> > wondering how I can solve this problem. Any suggestions? Help much
> > appreciated
> > >> I read the only article on Statalist about this error message, but it
> > really does not help me, and i dont really see how my data suffers from
> > these problems.
> > >
> > > Try centering your continously measured variables by period and then
> > > run -xtpcse, c(ar1)- again. Doing this comes at the cost of robbing
> > > your model of explaining the variance in your response variable that
> > > it would otherwise in a 'normal' model.
> > >
> > > --
> > > Clive Nicholas
> > >
> > > [Please DO NOT mail me personally here, but at
> > > <[email protected]>. Please respond to contributions I make in
> > > a list thread here. Thanks!]
> > >
> > > "My colleagues in the social sciences talk a great deal about
> > > methodology. I prefer to call it style." -- Freeman J. Dyson.
> > >
> > > *
> > > *   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/
> > >
> >
> > *
> > *   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/
>
> --
> Justina AV Fischer, PhD
> Senior Researcher
> Faculty of Economics
> University of Mannheim
>
> homepage: http://www.justinaavfischer.de/
> e-mail: [email protected]
> papers: http://ideas.repec.org/e/pfi55.html
>
>
> *
> *   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/

*
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