Hi all,

I have response measures corresponding to 2 patients. The structure is as
follows:

Patient 1:  Region 1             Region 2              Region 3
               S1 S2 S3 S4       S1 S2 S3 S4        S1 S2 S3 S4

Patient 2:  Region 1               Region 2            Region 3
                S1 S2 S3 S4       S1 S2 S3 S4        S1 S2 S3 S4

Each patient has 3 regions and each region has 4 sub-regions. (nested
design)

Fitting   *lme( Response ~ 1, random=~ Patient + Region +Subregion |
Patient/Region/Subregion )*
allows me to specify covariance structure for the 'sub-region' term.

But I'm trying to fit a random effects model of the form as I have only 1
observation per 'sub-region':
*lme( Response ~ 1, random=~ Patient + Region | Patient/Region )*

Is there a way I can specify a covariance structure like
the auto-regressive (to specify that correlation decreases with distance as
one moves from Subregion 1 to Subregion 4) for the 'sub-region' term only
as it is not included in my random effects model but I'd like to account
for the correlation in it?

Many thanks,
Angelina

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