Re: st:-expand- to adjust according to the sampling weight

[Steven Samuels <sjsamuels@gmail.com>]

Ms. Fu, the FAQ ask that you give the source for unofficial software.  
Kit Baum's -kdens2- does bivariate kernel density plots.  I don't know  
anything about the other commands you referred to.  Try the the  
example in the -help- for -kdens2-, first as written, then as expanded  
100 times.  ("expand 100") The two graphs will be very different:  
expansion doesn't work. The command you were looking for was "expand  
weight". As you say, expansion is equivalent to the use of frequency  
weights. The absence of frequency weight support in -kdens2-  is not  
an accident. Apparently there is no way to incorporate weights into a - 
kdens2- analysis.

Steven Samuels

sjsamuels@gmail.com
18 Cantine's Island
Saugerties NY 12477
USA
Voice: 845-246-0774
Fax:    206-202-4783




On Dec 20, 2010, at 9:11 PM, Amanda Fu wrote:

Dear Mr. Samuels,

Sorry for not making my question clear. I will keep in mind to provide
plenty of details in the future.

Here is my response to the questions you listed: The command is
-kdens2- , -spkde-,-spmap-. They allow neither frequency weights nor
sampling weights. The data structure is unbalanced panel data.There
are no clusters and strata. Simply only the sampling weight for each
individual exists. The purpose of my study is to estimate the
bivariate kernel density.

I thought I could expand the data based on sampling weights before
using those commands. I thought I could treat sampling weight similar
as frequency weight when expanding the data set:

.expand sweight

Even if this command is appropriate, it has a problem: the average
value for sampling weight in the data set is close to 3000. The
expanded data set would be too huge. Thus I was thinking to expand
with a smaller number, say

. sum sweight
. g new_weight=sweight/r(mean)
. expand new_weight

This way a number of observations will just remain unchanged after
expanding. I am not sure if this makes sense.

Thanks for your time!
Sincerely,
Amanda
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