Re: Covariate Models

From: Rik Schoemaker Date: June 13, 1997 technical Source: cognigencorp.com
From rs@chdr.leidenuniv.nl Fri Jun 13 00:46:37 1997 Subject: Re: Covariate Models Ralf, In your case, methods 1 and 2 will make no difference from a statistical perspective, > > method 1: V = THETA(1)+THETA(2)*WT > > method 2: V = THETA(1)+THETA(2)*(WT-70) > because subtraction of 70 merely results in a linear transformation. The only ('statistical') reason for doing this is computational, i.e. avoiding numbers that become too large. This is comparable to the reason behing the rescaling of parameters that NONMEM does prior to estimation. In the case of weights there is probably no reason to go to the trouble. In Raj's example, numbers becoming too large may certainly be a problem in his first method, which his second method solves. > > method1: TVV1 = THETA(1) * (WT)**THETA(2) > > method2: TVV1 = THETA(1) * (WT/70)**THETA(2) > Naturally, the values of theta(2) change, resulting in a different interpretation (or requiring rescaling back to the original situation). Regards, Rik Schoemaker

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Jun 11, 1997 Ralf Brueckner covariate models
Jun 11, 1997 Rene Braeckman Re: covariate models
Jun 11, 1997 Ferrin Harrison Re: covariate models
Jun 12, 1997 Pradhanr Re: covariate models
Jun 12, 1997 Ferdinand Rombout Antwort: RE: COVARIATE MODELS
Jun 12, 1997 Ralf Brueckner Covariate Models
Jun 12, 1997 Rene Braeckman Re[2]: covariate models
Jun 13, 1997 Vladimir Piotrovskij Gender as a covariate
Jun 13, 1997 Rik Schoemaker Re: Covariate Models
Jun 13, 1997 Rik Schoemaker Re: Re[2]: Covariate Models
Jun 13, 1997 Ferrin Harrison interpretable models
Jun 14, 1997 Ene Ette Re: Gender as a covariate
? Unknown Re[2]: Covariate Models
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