Re: st: Criteria for stratification??

[samirkc <samir.kc@bmg.eur.nl>]

Thanks Cox and Heather. Regarding Cox's comment, this is a EQ5D(European 
Quality of life) measurement. The result is in a continumm, but it is 
possible to have a maximum of 243 values in the range of -0.6 to 1.0 (it 
was mistake writing -1.6 earlier). We are using this EQ5D score as a 
measure of health effect of two kinds of treatment, we are using markov 
models  to capture the movements between different health states (based 
on EQ5D scores) in a life time perspective using multi-state life tables.
Regarding Heathers suggestion, Minimal important Difference (MID) or 
the clinically meaningful threshold, I have been thinking about it, It 
would be about .1, which will create too many states out of it. But this 
idea is under consideration, and I am working on it.
The question still is: Is there any statistical methods? what I am 
thinking is to start with 3 states arbitrarily defining cut points with 
at least .10 difference between two cutoffs and then lookin at some 
outcome (?? variance..standard error..)... then continuing to 
4..5..6..7. .. I am looking for some outcome which will be used in 
decision of number of states and cutoffs...
Thank  you and hope to get some response


SAMIR
Heather Gold wrote:


> If you have some knowledge or information about what increment poses a 
> clinically meaningful threshold, that could be used as a cutpoint 
> (e.g., every half point has an impact on a person's health somehow, 
> and so you create categories such as -1.5-(-1), -1-(-.5), -.5-0, 0-.5, 
> .5-1). Another option is to create "automatically determined" 
> categories such as tertiles but that is arbitrary, so you might want 
> to create, say, tertiles and quartiles and test if creating the 
> categories in that manner makes a difference.
>
> At 10:42 AM 6/16/2004, you wrote:
>
>
> > I have a discrete variable (health status)  which takes value from 
> > -1.6 to 1. The data consists of pre and post values of the variable. 
> > I want to categorize the variable in  3-7 categories in order to 
> > study the movement between categories . How can I do this? What 
> > Criteria should I use to determine the best categorization, in terms 
> > of 1. number of categories and, 2. cutoffs. Please respond.
> > Samir
> >
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