$ETAS, $PHIS

Specifies Initial Values for ETAS or PHIS.

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$ETAS  [[value1  [value2]  [value3] ... [valuen]]
        [FILE=filename  [FORMAT|DELIM =s] [TBLN=n]]  [ITERATION=n]]

$PHIS  [[value1  [value2]  [value3] ... [valuen]]
        [FILE=filename  [FORMAT|DELIM=s1] [TBLN=n]]  [ITERATION=n]]

;# EXAMPLE
 $ETAS 0.4 3.0 3.0 5.0
 $PHIS 0.4 3.0 3.0 5.0
 $ETAS FILE=myprevious.phi FORMAT=s1pE15.8 TBLN=3
 $PHIS FILE=myprevious.phi FORMAT=s1pE15.8 TBLN=3
 $ETAS FILE=myprevious.iph TBLN=3 ITERATION=123

NONMEM describes the use of these records with messages in the report file such as the following:

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LOADED    3 PHI/ETA ITEMS FROM CONTROL STREAM

Discussion

By default, the initial value used for ETA's in the Estimation Step search is 0. The $ETAS and $PHIS records provide different initial estimates. Optional.

Options

There are two forms:

$ETAS value1 [value2] [value3] …[[valuen]

All of the subjects in the data set will be given these initial values of ETAs. If fewer values are listed than the number of ETAs in the problem, the value 0 will be used for the remaining ETAs. Any real value (positive, negative, zero) may be specified.

When the record is $PHIS, values are entered as phi values, convenient for EM methods. The eta values will then be evaluated as eta(i)=phi(i)-mu(i) for each eta, where mu(i)=mu_i is evaluated according to their definitions in the $PK section.

FILE=filename FORMAT=s TBLN=n ITERATION=n

Uses initial ETAs and/or phis for an entire set of subjects from a file .phi, .phm (in the case of mixture problems) of a previous analysis, or .iph file.

With FORMAT, s defines the delimiter [,|s(pace)|t(ab)] followed by a Fortran format specification. The default is s1PE12.5. FORMAT should at least have the delimiter appropriate to read the file. May also be coded DELIM. For more details, see the format help:

TBLN is the table number in the file. If TBLN is not specified, it defaults to 1, i.e., the first set of ETAs/phis are brought in.

ITERATION is the iteration number in a .iph file (not relevant for .phi or .phm file). As a .iph file has both ETA() and PHI() items, ETA()s will be selected for a $ETAS record, and PHI() will be selected for a $PHIS record. The first ITERATION>0 is selected, unless a particular iteration is specified.

In matching the ETAs/phis to the data set given in $DATA of the control stream file, the attempt will be to match ID numbers rather than subject numbers, if an ID column in the file exists, which it will, if you are using a .phi or .phm file generated from a previous nonmem analysis. The phc/etc variances will also be brought in.

One purpose to bringing initial eta/phi and etc/phc values is you can readily resume an analysis, if an MSF file was not set up in the previous analysis (the MSF file system is still the most complete information transfer for resuming an analysis.

Usage

The ETAs from $ETAS and $PHIS can be used in several ways.

In METHOD=0 (FO), they are ignored, because FO is specifically designed as a first order Taylor series approximation process centered around eta=0.

In METHOD=1 (FOCE), they are ignored unless MCETA>0. When MCETA>0, then various starting ETAs are tested, including a set from $ETAS, when available.

In Bayes, SAEM, IMP MAPITER=0 they are used as the starting ETAs.

In MAP estimation methods, such as METHOD=1, or ITS, or IMP MAPITER>0, or IMPMAP, and if MCETA>0, then these ETAs are one of the initial eta vector positions tested (during the first iteration), and the one giving the lowest OBJ is then selected.

In cases where FNLETA=2, the estimation step is skipped, and ETAs inputted from $ETAS are treated as if they were the final result of an estimation.

One purpose to bringing initial eta/phi and etc/phc values is you can readily resume an analysis, if an MSF file was not set up in the previous analysis (but note that the MSF file system is still the most complete information transfer for resuming an analysis).

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$PHIS FILE=etafile3_phi.phm FORMAT=S1PE15.7  TBLN=3

Or, use FNLETA=2 to use the ETAs that were brought in to evaluate predicted values, without performing a new population estimation:

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$ETAS FILE=etafile_phi.phi FORMAT=S1PE15.7  TBLN=6

$EST METHOD=1 INTERACTION NSIG=3 PRINT=1 FNLETA=2