RE: st: Age-specific reference intervals (xrigls) - no equation for SD?

[Sofia Ramiro <sofiaramiro@hotmail.com>]

> > Dear Statalist members,
> >
    I sent this question some days ago but did not get any answer, so I send it again. Please let me know if the problem is my question not being clear enough or missing some information. 
> > I am trying to define age-specific reference intervals with the command xrigls.

> >
> > However, when running it, for some of the variables for which I want to define the age intervals I get an equation for the mean (with the corresponding power), but no equation for the SD - example below. I don't understand why. Can any of you explain this?
> > Are the values derived without the SD equation also right?
> > I don't understand why in the 1st table (FP powers) the change appears always as 0. I inspected the data and there is variation in this variable and throughout the different ages.
> >
> > Thanks
> >
> > Sofia
> >
> >
> >
> > . xrigls schober15 age if sample==1, fp(m:df 4,s:df 2) centile(2.5 10 25 75 90 97.5) detail
> >
> > --- FP Powers ---
> > Cycle Mean SD Deviance Change Residual SS
> > -----------------------------------------------------------------
> > 0 1 1217.262 0.000 509.4298
> > 1 1 1217.262 0.000 509.4298
> > 2 1 1217.262 0.000 509.4298
> >
> > Final deviance = 1217.262 (393 observations).
> > Power(s) for mean curve = 1.
> >
> > Regression for mean curve
> > -------------------------
> > (sum of wgt is 3.4287e+02)
> >
> > Source | SS df MS Number of obs = 393
> > -------------+------------------------------ F( 1, 391) = 24.05
> > Model | 31.3308787 1 31.3308787 Prob > F = 0.0000
> > Residual | 509.429806 391 1.30288953 R-squared = 0.0579
> > -------------+------------------------------ Adj R-squared = 0.0555
> > Total | 540.760685 392 1.37949154 Root MSE = 1.1414
> >
> > ------------------------------------------------------------------------------
> > schober15 | Coef. Std. Err. t P>|t| [95% Conf. Interval]
> > -------------+----------------------------------------------------------------
> > age | -.0203814 .0041562 -4.90 0.000 -.0285528 -.01221
> > _cons | 7.191451 .1913316 37.59 0.000 6.815284 7.567619
> > ------------------------------------------------------------------------------
> >
> >
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