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st: RE: Re: RE: CASE-CONTROL STUDY


From   "Kieran McCaul" <kamccaul@meddent.uwa.edu.au>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: Re: RE: CASE-CONTROL STUDY
Date   Mon, 16 Mar 2009 06:35:42 +0900

I wasn't suggesting that you design a prospective study, I was merely pointing out that if you already have the data you will gain nothing by matching.  If you match you will throw away data that you already have and therefore lose power.

Now if you wish to do a case-control study and your definition of a case is a condition that predominates in geriatric patients, then younger patients will not add significantly to your study because they will be far more likely to be a control than a case.  This is not, however, an argument for matching on age.  You simply need to restrict the analysis to patients older than a certain age, patients 65 years and older for example.  While this would reduce your sample size, the loss of power would be minimal because the younger patients would have contributed little to the analysis anyway.



______________________________________________
Kieran McCaul MPH PhD
WA Centre for Health & Ageing (M573)
University of Western Australia
Level 6, Ainslie House
48 Murray St
Perth 6000
Phone: (08) 9224-2140
Fax: (08) 9224 8009
email: kamccaul@meddent.uwa.edu.au
http://myprofile.cos.com/mccaul 
http://www.researcherid.com/rid/B-8751-2008
______________________________________________
Epidemiology is so beautiful and provides such an important perspective on human life and death, 
but an incredible amount of rubbish is published.  Richard Peto (2007) 

-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Ishay Barat
Sent: Monday, 16 March 2009 1:52 AM
To: statalist@hsphsun2.harvard.edu
Subject: st: Re: RE: CASE-CONTROL STUDY

Dear Kieran and David



There can be lots of arguments why one designs backwards study and not 
forward one. In my case, I am responsible for a lot of patients, going 
through my department, and need form time to time to have quality control of 
our patients management. It would have been nice to have a quarter of a 
million $ and 3 years time to carry on a study, but that's not reality.



Sorry.



And now for your question.



As my objective is geriatric patients, and my data includes general inter 
medicine ward cliental I like to reduce the noise younger and far healthier 
patients introduces into my data.

By matching some crucial parameters like age, sex, medication and disease, I 
may get answers to my questions.



As to my anagram. It is just for fun and nothing else.



As to the reference to 
http://personalpages.manchester.ac.uk/staff/mark.lunt/optmatch.html

I installed the files, but can not find the command in the menus.




*¸..· ´¨)) -:¦:-        *
    ¸.·´ .
  (( -:¦:- * Ishay *  -:¦:-
    ´·..          ..·´
               ((¸¸.·´* -:¦:-

_________________________________________________________-


> Matching is an element of the design of a study, planned before the data 
> is collected, and should be done for efficiency, not control.
> If you already have the data, you gain nothing by matching.  You have a 
> sample size of 2,500.  If you match these data in the way you have 
> indicated, you will end up with a matched sample size of 1,200.  Why would 
> you want to discard over half of your data?
>
> You should analyse the data as they are and control for age, sex, etc in 
> the analysis.
>
>
> ______________________________________________
> Kieran McCaul MPH PhD
> WA Centre for Health & Ageing (M573)
> University of Western Australia
> Level 6, Ainslie House
> 48 Murray St
> Perth 6000
> Phone: (08) 9224-2140
> Fax: (08) 9224 8009
> email: kamccaul@meddent.uwa.edu.au
> http://myprofile.cos.com/mccaul
> http://www.researcherid.com/rid/B-8751-2008
> ______________________________________________
> Epidemiology is so beautiful and provides such an important perspective on 
> human life and death,
> but an incredible amount of rubbish is published.  Richard Peto (2007)
>
> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu 
> [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Ishay Barat
> Sent: Sunday, 15 March 2009 1:28 AM
> To: statalist@hsphsun2.harvard.edu
> Subject: st: CASE-CONTROL STUDY
>
> HELLO
>
>
>
> I've got a data set containing about 2500 patients, of which 300 have my
> interest (Group A).
>
> I would like to extract a sample of 900 patients (Group B) out of the data
> set that match Group A in age, sex and some other parameters. A Classical
> Case-Control study with 3 controllers for each case.
>
>
>
> Is anybody have a clue how the syntax look like??
>
>
>
>
>
>
> *¸..· ´¨)) -:¦:-        *
>    ¸.·´ .
>  (( -:¦:- * Ishay *  -:¦:-
>    ´·..          ..·´
>               ((¸¸.·´* -:¦:-
>
> *
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