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st: repost mixed effects fractional polynomial


From   "William Johnson" <wojohnso@umn.edu>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: repost mixed effects fractional polynomial
Date   Tue, 24 Jan 2012 11:40:07 -0600

I am using the code at the end of this post to fit a two degree mixed
effects fractional polynomial model.

I can't get the code to allow ONLY the first degree to have mixed effects.
My thought was that (names) should be replaced with (p1) on the random
effects side of the xtmixed code, because the power combinations that
fracpolypowers creates are called r(p1) and r(p2), but this doesn't work. 

Does anyone have any suggestions?

Will Johnson 

// Store FP2 powers in local macros
fracpoly_powers, degree(2)
local np = r(np)
forvalues j = 1 / `np' {
                local p`j' `r(p`j')'
}
// Compute deviance for each FP model with covariate age gen x = age gen y =
bmi local devmin 1e30 forvalues j = 1 / `np' {
                qui fracgen x `p`j'', replace adjust(mean)
                qui xtmixed y `r(names)' || id: `r(names)',
covariance(unstructured) mle
                local dev = -2 * e(ll)
                if `dev' < `devmin' {
                                local p `p`j''
                                local devmin `dev'
                }
       di "powers = `p`j''" _col(20) " deviance = " %9.3f `dev'
}
di _n "Best model has powers `p', deviance = " `devmin'

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