[R list package] Computational Problems Using 'List' Package

[Kosuke Imai]

Does your data pass the design test we've developed?  Sometimes, the skewed
data leads to this type of problems.  Another possibility is to use a
Bayesian model, which is available through ictregBayes().

Kosuke Imai
Department of Politics
Princeton University
http://imai.princeton.edu


On Tue, Feb 25, 2014 at 6:44 PM, David Szakonyi <ds2875 at columbia.edu> wrote:

> Hello!
>
> I've been analyzing a two treatment list experiment that has been properly
> randomly assigned.
>
> I just ran the following regression with one simple explanatory bivariate
> variable (gender), but received the following error:
>
> > ml.resultsnp <- ictreg(outcome ~ male, data = true_subsetnp, treat =
> "treatstatnp", J=4, method = "ml")
>
> Error in solve.default(-MLEfit$hessian) :
>   system is computationally singular: reciprocal condition number =
> 7.02376e-18
>
> I then added an additional covariate (logged age), and the model
> converges, but with exploding standard errors:
>
> Item Count Technique Regression
>
> Call: ictreg(formula = outcome ~ male + lage, data = true_subsetnp,
>     treat = "treatstatnp", J = 4, method = "ml")
>
> Sensitive item (1)
>                 Est.    S.E.
> (Intercept)  3.94811 4.15077
> male        -1.43966 1.21671
> lage        -1.78966 1.14337
>
> Sensitive item (2)
>                  Est.       S.E.
> (Intercept)  -7.93707   10.31522
> *male        -16.06552 2965.82521*
> lage          0.99201    2.63957
>
> Control items
>                 Est.    S.E.
> (Intercept)  0.21267 0.25312
> male         0.00017 0.05277
> lage        -0.04225 0.06603
>
> Log-likelihood: -2039.366
>
> Number of control items J set to 4. Treatment groups were indicated by '1'
> and '2' and the control group by '0'.
>
> A variety of other model specifications return very similar results:
> either failing to converge/compute or returning point estimates and very
> large standard errors (sometimes nearly exactly the same values for not at
> all correlated variables).
>
> Does anyone have any suggestions about what might be going wrong?
>
> Thanks,
>
> David
>
>
> --
> David Szakonyi
> Ph.D Candidate - Comparative Politics
> Columbia University
> ds2875 at columbia.edu
>
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