To plot the average district vote by
the probability of winning the election. The probability-votes curve is
plotted as a solid line, and plus and minus one standard error are plotted on
this graph as dotted lines, if PLOT is chosen. If the LIST option is chosen,
the plot is not done, but the values that would be plotted are instead printed
on the screen and the output file in a convenient table.
The three uses to which you might want to put a PVCURVE statement:
- Evaluation of a past electoral system using data from that
election. To do this, specify YVOTE with a variable name and XVARS
(and no XNEW statement) before PVCURVE.
- Prediction of a future election, or under a new redistricting plan.
To do this, input data from the most recent election available by specifying
YVOTE with a variable, and XVARS. Then issue a REG; command or run one
of the analysis procedures (such as PVCURVE). Finally, to do the prediction,
specify YVOTE year PREDICT, and use XNEW (without XVARS) to identify the
explanatory variables you are using for prediction, both before the PVCURVE
command.
- Counterfactual evaluation of a situation that might have happened
in a past election. To do this, specify YVOTE with a variable, XVARS, and
XNEW. XNEW indicates the counterfactual you wish to evaluate. For example, if
you set your incumbency status variable to represent all seats as open with
XNEW, then PVCURVE will report a prediction of what these four statistics would
be if no incumbents were to run for reelection.
Gary King
2006-01-07
