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Re: AW: AW: st: error message "too many weights"


From   Steve Samuels <sjsamuels@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: AW: AW: st: error message "too many weights"
Date   Tue, 27 Mar 2012 05:13:48 -0400


Jette Kellerhoff-

Your use of the words "panel" and "wave". suggests that you have survey data. If so, the weight should be designated a probability weight (pweight). At a minimum then, you need  [pweight = gew] in the -stset- statement. This will give you properly weighted estimates of descriptive statistics like the survival curve. 
 
If the survey had a multi-stage design and you intend to run regression commands like -stcox-, you will need to -svyset- the data. If you don't, standard errors and p-values will be wrong. The -svyset- statement has the form:

*********************************************
svyset psu_var [pw = gew], strata(stratum_var)
*********************************************
        
After that, use the -svy:- prefix for -stcox- and -streg-. 

 If you are planning  multiple failure time analyses and weights are constant within id, then you will be omit the cluster(id) option in -stset-.  That won't matter, because standard errors will be based on the survey design.  

If weights are not constant within ID, -stset- will complain.  So check first.  You have multiple spell data, apparently, and I'm not sure of your data structure. But a generic solution is to add an enter() option to the -stset- statement and omit the id() option. The code would be something like:

*************CODE BEGINS*************
svyset psu_var [pw = gew], strata(stratum_var)
stset  tfp , fail(event indicator) enter(start time for spell) exit(time.)
svy: stcox   // etc.   
**************************************

 
Steve
sjsamuels@gmail.com




See also: http://www.stata.com/statalist/archive/2008-10/msg01494.html.  

On Mar 26, 2012, at 5:03 AM, Nick Cox wrote:

I could tell you how to force non-integers to integers but I fear that
would be telling how to force your problem into an incorrect or
dubious application of -st-.

I am in no sense an expert on survival analysis, so I won't comment
further. This may or may not be enough information for someone
competent in that field to get a sense of what your real problem is
and give better advice.

Nick

On Mon, Mar 26, 2012 at 9:44 AM, Jette Kellerhoff <jettek82@aol.com> wrote:

> For each subject exists a weight (variable gew), which identifies the real
> abundance pattern in time. The computed values of the variable gew are the
> result of the real abundance pattern multiplied by the probability to stay
> in the panel. So in many cases the results are not integers. How to create
> integers?

Nick Cox

> I could tell you about Stata. But you really need to explain what the
> variable -gew- is, why some values are not integers, and why you want
> to treat them as frequency weights.

On Sun, Mar 25, 2012 at 6:50 PM, Jette Kellerhoff <jettek82@aol.com> wrote:

>> There are some non-integer values. How to create integers?

Nick Cox

>> The implication is that your variable -gew- contains non-integer
>> values. Is that true?
>> 
>> . list gew if gew != floor(gew)
>> 
>> fweights indicate frequencies, which must be integers.

On Sun, Mar 25, 2012 at 6:09 PM, Jette Kellerhoff <jettek82@aol.com>

>>> I removed the first bracket, but the error message is still the same: may
>>> not use noninteger frequency weights
>>> stset tfp [fweight = gew], id(hhnrakt) f(des=2 4 6 8 10 12) exit(time .)

Steve Samuels

>>> You did not follow my advice to look at the examples. You only removed
> the
>>> last bracket; the beginning "[" of the second pair remains.

On Mar 25, 2012, at 12:40 PM, Jette Kellerhoff wrote:

>>> Thanks for your advice. If I remove the brackets, I get the following
>> error
>>> message may not use noninteger frequency weights. I don't understand it,
>>> because fweights are allowed in the stset-command.
>>> The do-file:
>>> stset tfp [fweight=gew] [ ,id(hhnrakt) f(des=2 4 6 8 10 12) exit(time.)

Steve Samuels

>>> I should add that in the -help- for -stset-, the brackets indicate where
>>> options, if any, should go. Before running an unfamiliar command, always
>>> look at the examples at the bottom of the help screen or in the manual.

>>> Remove the second pair of brackets in your -stset- statement. They are
> not
>>> legal Stata syntax.

On Mar 22, 2012, at 3:18 PM, Jette Kellerhoff wrote:

>>> Sorry for the impatientness, but I have to solve the problem very soon.
>>> The case:
>>> - 4841 subjects with multiple record per subject (max 4 records)
>>> - for each subject exists a weight, which identifies the real abundance
>>> pattern in time
>>> 
>>> I used the following do-file:
>>> gen des =tfin~=ti
>>> 
>>> gen tf = tfin-tstart+1
>>> 
>>> gen org=1+2*(spell-1)
>>> replace des=org
>>> replace des=org+1 if tfin<ti
>>> gen tfc=tstart if spell==1
>>> replace tfc=tfc[_n-1] if spell~=1 & hhnrakt==hhnrakt[_n-1]
>>> gen tsp = tstart-tfc
>>> gen tfp = tfin-tfc+1
>>> stset tfp [fweight=gew] [ ,id(hhnrakt) f(des=2 4 6 8 10 12) exit(time .)]


Richard Herron

>>> Jette, can you provide a reproducible example? That may help diagnose
>>> your problem. Can you reproduce the error with -sysuse- data or
>>> provide your console output, please?

On Thu, Mar 22, 2012 at 14:34, Jette Kellerhoff <jettek82@aol.com> wrote:

>>>> how to deal with weights according to survival data analysis? If I use
>>>> fweights according to stset command, I get the error message "too many
>>>> weights". Does anyone have any suggestions?
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