Calculation of intra-subject CVs in replicate design [General Sta­tis­tics]

posted by d_labes  – Berlin, Germany, 2008-03-03 13:05 (5752 d 03:03 ago) – Posting: # 1654
Views: 15,639

Hello David,

i agree with your assignment of the intraindividual error terms.

❝ Covariate Parameter Estimates

❝ Cov Parm Subject Group Estimate

❝ FA(1,1) Subject 0.5928 <---- (sig_BT, the between-subject standard

❝ deviation for the Test product)

❝ FA(2,1) Subject 0.4968 <---- (sig_BR, the between-subject standard

❝ deviation for the Reference product)

❝ FA(2,2) Subject 2E-17 <---- (sig_D, the subject-by-formulation

❝ interaction term)

But your assignment of the FA(i,i) terms to the interindividual (co)variances is not correct i think.
Think of the G matrix (using your notation):
   G(1,1) = sig_BT2
   G(2,2) = sig_BR2
   G(1,2) = rho*sig_BT*sig_BR

Futher it is defined (subject-by-formulation interaction variance)

The FA0(2) parameterization of the G-Matrix reads

Confer to the SAS documentation for this.
By the way: G(1,1) = sig_BT2 is only valid, if your coding of test treatment preceedes that of the reference.

Thus with some algebra you obtain

Thus your assignment of FA(2,1) is only valid if rho=1 which implies FA(2,2)=0.
In that case the subject-by-formulation interaction variance is



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