[Limdep Nlogit List] Plotting Confidence Intervals
Mikołaj Czajkowski
miq at wne.uw.edu.pl
Tue Sep 16 22:02:01 EST 2008
Dear All,
I am running a Box-Cox model to estimate elasticities of WTP which would
vary with income. I can plot the elasticities, but I would also get the
confidence intervals (e.g. using K&R method) plotted.
The model looks like this:
(WTP)@THETA = b2*1 + b1*(HINCOME)@LAMBDA
where:
@ is a Box-Cox transformation
LAMBDA and THETA are ML estimates for transformation parameters
WTP and HINCOME is self explanatory
After estimating the model I am able to plot the changes in elasticity
as a function of HINCOME by either:
create; elast=b(1)*hincome^(lambda)*((b(2)+b(1)*hincome)@lambda)^(-lambda)$
plot; lhs=hincome; rhs=elast; fill$
(which uses sample-based HINCOME)
or by:
calc ; bet1=b(1)
; bet2=b(2)$
sample; 1$
fplot; FCN=bet1*hi^(lambda)/(theta*(bet2+bet1*hi at lambda)+1); labels=hi;
start=500; plot (hi); pts=1000; limits=100,5000$
(which simulates any hincome between the given limits).
This works ok.
However, is there a nice way to plot confidence intervals of the
elasticities? The only thing that comes to my mind is writing a
procedure that would use K&R technique to find 0.05 and 0.95 percentile
of the elasticity distribution for each of the points from the income
range. This is possible, but it is probably the long way...
I would be grateful for any ideas on how to possibly make it easier.
Thank you in advance,
--
Mikołaj Czajkowski
Warsaw Ecological Economics Center
Warsaw University
http://www.woee.pl/
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