Statalist


[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: st: What does 'ssss' mean with replication dots?


From   jpitblado@stata.com (Jeff Pitblado, StataCorp LP)
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: What does 'ssss' mean with replication dots?
Date   Fri, 06 Nov 2009 17:59:40 -0600

Philip Burgess <philip.burgess.uq@gmail.com> is using -svy jackknife- and
noticed that there were 's' characters sprinkled in with the dots displayed
for each jackknife replicate:

> I have two independent complex survey designs, one with 30 JK
> replicate weights (survey conducted in 1997), the other with 60
> (survey conducted in 2007).
> 
> I have combined these files in a manner similar to the Californian
> Health Interview Surveys - http://www.chis.ucla.edu/methodology.html
> (see the Methodology Paper on Examining Trends ... - this has detailed
> instructions regarding how to combine such data with STATA).
> 
> So, my combined file has 90 replicate weights.
> 
> I svyset with the following command:
> 
> - svyset [pweight=mhsfinwt], jkrweight(wpm0101 - wpm0190,
> multiplier(1)) vce(jackknife) mse -
> 
> When processing this design, for say, estimating propotions for the two surveys:
> 
> - svy jackknife : proportion mhpsyo12, over(nsmhwb)
> (running proportion on estimation sample)
> 
> Jackknife replications (90)
> ----+--- 1 ---+--- 2 ---+--- 3 ---+--- 4 ---+--- 5
> ..................................................    50
> ..........ssssssssssssssssssssssssssssss
> 
> What does the 'ssss...' mean?

's' is one of those special codes like 'e' and 'n'; 'e' and 'n' are documented
with the -dots- option in -[SVY] svy jackknife-.

's' indicates that the corresponding replicate contributes nothing to the
variance estimate because the omitted PSU does not overlap with any
observations in the subpopulation.  For example, in the delete-1 jackknife
this will occur when a PSU is in the estimation sample but is outside the
subpopulation sample.

When replicate weight variables are -svyset-, this can only happen if the
values of the replicate weight variable are equal to the original sampling
weight within the estimation sample.

Given Philip's -svyset- command, it appears that -- within the estimation
sample -- the last 30 replicate weight variables do not differ from the
-mhsfinwt- variable.

In a future update, we will modify the help file for -svy jackknife- to
document the 's' character (like the 'e' and 'n' "dots").

--Jeff
jpitblado@stata.com
*
*   For searches and help try:
*   http://www.stata.com/help.cgi?search
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/



© Copyright 1996–2014 StataCorp LP   |   Terms of use   |   Privacy   |   Contact us   |   What's new   |   Site index