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Re: st: RE: stored p-value of sts test


From   Steve Nakoneshny <scnakone@ucalgary.ca>
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   Re: st: RE: stored p-value of sts test
Date   Fri, 20 Jan 2012 12:55:10 -0700

Thanks Nick.

I now have some reading to do before going to the fun part of coding it up.

Much obliged,
Steve

On 2012-01-20, at 11:33 AM, Nick Cox wrote:

> You'll have to work out the P-value from the other r-class results to do this. Look up the chi-squared functions under -help density functions-. 
> 
> By the way, there seems some confusion here. 
> 
> -sts- does accept -if- qualifiers (not statements), which select observations to be used. 
> 
> But you want to see a graph conditional on whether the result is significant. That's a completely different -if-, the -if- command. 
> 
> People often confuse -if- and -if-; if so, it is not surprising.
> 
> FAQ     . . . . . . . . . . . . . . . . . . . . .  if command vs. if qualifier
>        . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  J. Wernow
>        6/00    I have an if or while command in my program that
>                only seems to evaluate the first observation,
>                what's going on?
>                http://www.stata.com/support/faqs/lang/ifqualifier.html
> 
> Schematically you want 
> 
> sts test `x', logrank
> <calculate P-value> 
> if <P-value> < 0.05 { 
> 	sts graph, by(`x') tmax(60)
> 	graph save `x', replace
> } 
> 
> (Consider sprinkled here mild disquiet and strong cautions about using significance tests in this way from the ghost of R.A. Fisher, an early Hogwarts student.) 
> 
> Nick 
> n.j.cox@durham.ac.uk 
> 
> Steve Nakoneshny
> 
> I am performing some exploratory analyses in an stsetted dataset using Stata 11.2 for Mac.
> 
> As part of a loop, I coded the following:
> 
> -- start code --
> 
> sts test `x', logrank
> sts graph, by(`x') tmax(60)
> graph save `x', replace
> 
> -- end code --
> 
> My local `x' comprises 18 variables, so the loop generates more graphs than I actually want to save. Looking at the help, I see that -sts graph- accepts -if- statements. What I would like to do is only graph (and save) where -sts test- is statistically significant (p<0.05). According to -help-, -sts test- doesn't save the p-value in r().
> 
> What I would like to know is whether or not the p-value is stored somewhere else (if at all) or if there is an alternate workaround I can implement.
> 
> 
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