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Re: st: gllamm with pweights


From   sjsamuels@gmail.com
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: gllamm with pweights
Date   Fri, 17 Jul 2009 11:27:39 -0400

Rebecca, I didn't follow the original  thread, so I apologize.  As
there was no sampling of your level-two units,  you do not need
sampling weights for them, nor, therefore, the weights computed by
Chantala's code.  We could have been more helpful  if you had
described the original design. What was it, and what were the PSUs?
The PSUs are the units which should be designated as  clusters in
-gllamm-.  They need not be part of the two-level model, but might be
interesting as units in a three-level model.

You can use the original sampling weights,  but perhaps you have
enough information to post-stratify the weights for individuals, for
example by gender and state. This is less necessary if gender is a
predictor for your multi-level model.

Good luck

Steve




On Thu, Jul 16, 2009 at 3:08 PM, Kanter, Rebecca<rkanter@jhsph.edu> wrote:
> Thanks Steven, these resources are a big help.
>
> I am now trying to apply this method to my 2 level model (L1 = individual L2 = urban or rural part of state they live in; 64 units based on 32 states).
>
> In the method by Chantala et al, if I am interpreting this correctly...the PSU takes on a new meaning here (from the original complex survey design)...
>
> whereby PSU_wtj = 1 / Pr(urstate j selected) --> so if I am including all urban and rural parts of states (i.e. all 64 units that in turn make up the 32 states in a country) then is 1 for every urstate ?
>
> Furthermore, then, if FSU_wt i|j = 1 / Pr(person i selected / urstate j selected) then is FSU_wt i|j = 1 / Pr ( (1 / total number of people in urstate j) / 1) as in their example with schools = j each "student selected from school j will have a sampling weight equal to the number of students within school j represented by that student."?
>
> And in the end the original survey individual pweight is not used?
>
> Thanks so much for all your help,
> Rebecca
>
>
> ___________________________________________
> Rebecca M. Kanter
> PhD Candidate
> Johns Hopkins Bloomberg School of Public Health
> Department of International Health
> Center for Human Nutrition
> ________________________________________
> From: owner-statalist@hsphsun2.harvard.edu [owner-statalist@hsphsun2.harvard.edu] On Behalf Of sjsamuels@gmail.com [sjsamuels@gmail.com]
> Sent: Thursday, July 16, 2009 12:24 PM
> To: statalist@hsphsun2.harvard.edu
> Subject: Re: st: gllamm with pweights
>
> --
>
> Also, see: http://www.stata.com/meeting/4nasug/Chantala.ppt and
> http://www.cpc.unc.edu/restools/data_analysis/ml_sampling_weights.
> These contain links to the Stata program -pwigls- which will scale the
> weights.  Rabe-Hesketh and Skrondal (2006), the second citation that
> Stas listed, compute the  "Method 1" weights by hand and illustrate an
> analysis in GLLAMM.
>
> Rabe-Hesketh, S. & Skrondal, A. (2006). Multilevel modelling of
> complex survey data. Journal of the Royal Statistical Society: Series
> A (Statistics in Society), 169(4), 805-827.
>
> On Thu, Jul 16, 2009 at 12:28 PM, Stas Kolenikov<skolenik@gmail.com> wrote:
>> Oh, I see. With 64 second level units, you are in a much better shape.
>> I would probably have an urban/rural dummy as an explanatory variables
>> for those second levels with -feq- option.
>>
>> If you sum up the weights, you are using the weights twice. And that's
>> hardly a great idea: you are overcompensating for unequal
>> probabilities of selection, if there were any. Were these
>> states/ruran/urban areas selected via a sampling procedure? Or what
>> you have is a complete list? In the latter case, you surely would need
>> to specify unit weights at the second level.
>>
>> On the issue of weights in multilevel models, see:
>> http://www.citeulike.org/user/ctacmo/article/711637,
>> http://www.citeulike.org/user/ctacmo/article/850244,
>> http://www.citeulike.org/user/ctacmo/article/3158754. There's probably
>> more by now, but I am not tracking this literature very closely.
>>
>> On Thu, Jul 16, 2009 at 11:18 AM, Kanter, Rebecca<rkanter@jhsph.edu> wrote:
>>> Hi Stan and statalist,
>>>
>>> Regarding my second level it is more than 2 values...as there are 32 states in the country...that makes 64 values (or areas/clusters that i illustrate via one variable called urstate...e.g. if urstate=1 it is the urban area of the 1st state and if urstate=33 it is the rural area of the 1st state and so on) if one divides each state into its urban and rural areas, respectively. Each one I want to take its own intercept and slopes etc to better account and visualize the urban and rural differences in the country....
>>>
>>> Thus, is it better to sum the individual weights per urstate (1-64) or let all weights for this second level equal one and keep my individual pweights as is for the individual level (level 1)?
>>>
> ________________
>>> From: owner-statalist@hsphsun2.harvard.edu [owner-statalist@hsphsun2.harvard.edu]
>>> On Wed, Jul 15, 2009 at 5:37 PM, Kanter, Rebecca<rkanter@jhsph.edu> wrote:
>>>> Hi,
>>>>
>>>> I am running 2 level multi-level models using gllamm. Level one is individuals and Level two is either the urban or rural part of the country's state (i.e. urstate).
>>>>
>>>> I would like to use the survey pweights I have...I only have pweights for the individual level (adul_sr), but it seems that you need pweights for all levels specified in gllamm (?) so this is what I did to create pweights for urstate based on these weights:
>>>>
>>>> collapse (sum)  sadul_sr=adul_sr , by(urstate)
>>>>
>>>> then I merged them to the rest of my dataset
>>>>
>>>> and made this weight for the gllamm:
>>>>
>>>> *MLM-level pweights
>>>> generate pwadulsr1=adul_sr
>>>> *urstate summed adul_sr
>>>> generate pwadulsr2=sadul_sr
>>>>
>>>> Then ran the most basic random-intercept only (around urstate) in gllamm and get the follow error below and am assuming it is a pweight problem but I do not know where the problem is coming from so if anyone has insight that would be much appreciated. Thanks so much!
>>>>
>>>> (note: diettag==1 & exwt==1 is the subpopulation i want to look at for this series of models)
>>>>
>>>> gllamm bmi2 if diettag==1 & exwt==1, i(urstate) pweight(pwadulsr) adapt nip(15)
>>>>
>>>> Running adaptive quadrature
>>>>
>>>> Convergence not achieved: try with more quadrature points
>>>>
>>>>
>>>
> Steven Samuels
> sjsamuels@gmail.com
> 18 Cantine's Island
> Saugerties NY 12477
> USA
> 845-246-0774
>
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-- 
Steven Samuels
sjsamuels@gmail.com
18 Cantine's Island
Saugerties NY 12477
USA
845-246-0774

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