this link will explain how to compute simulations of quantities of
interest from more than one setx value of X:
http://gking.harvard.edu/clarify/docs/node21.html
The example in this link of quantities correspond to rows of X, but you
could modify it for different values.
However, if you need to compute correlations among the different
quantities of interest, then you need to produce the simulations jointly,
by reusing the simulations of beta (which induces the correlation). I
don't believe the code in this link does that, so you'd need to modify it,
which I think ought to be fairly straightforward.
Another option is Zelig (
http://gking.harvard.edu/zelig), which will do
what you want automatically.
Gary
---
Gary King
Institute for Quantitative Social Science
Harvard University, 34 Kirkland St, Cambridge, MA 02138
http://GKing.Harvard.Edu, email: King(a)Harvard.Edu
Direct 617-495-2027, Assistant 495-9271, eFax 812-8581
On Thu, 21 Apr 2005, Tobias Stark wrote:
Dear Professor King,
I am student of political science at the University of Mannheim, Germany. In
my current research I am concerned with the explanation of vote over
reporting and therefore I have a question regarding Clarify. Since you are
one of its authors, I hope you have an idea to solve my problem.
Using sample data I estimated a logistic regression to model whether or not
the respondents voted in the last three elections. Afterwards, I used Clarify
to receive predicted values for three specific combinations of the
independent variables (the difference is the year of election). To identify
the size of vote over reporting, I subtracted the real turnout of each
election year from my predicted values. As the values of the true turnout lie
within the confidence interval of the predicted values, these differences are
not significant.
The next step should be a test, if the differences between the true turnout
and my predicted turnout for the three election years are statistical
significant different. Therefore, my idea was to perform a t-test for
dependent samples. To do this, I need the variance of each estimator and the
covariance of the ones I would like to compare. However as far as I know,
Clarify offers the variance of a predicted value, but not the covariance
between two predicted values (for two election years). Do you have any idea
how I could get this covariance?
Thanks in advance.
Sincerely yours,
Tobias Stark
________________________________________________________________
Tobias Stark
Bismarckstr. 49
67059 Ludwigshafen
Germany
0049 (0)621 181 3433
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