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 |                     INTRA AND INTER-INDIVIDUAL                     |
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 MEANING: Types of random errors
 CONTEXT: NONMEM terminology

 DISCUSSION:

 Random  intra-individual ("within an individual") and inter-individual
 ("between individuals") variability are terms that are  used  in  dis-
 cussing NONMEM output.

 Case 1. When the data are population
      Random  inter-individual  variability  refers  to the unexplained
      difference between individuals' parameter values and the  typical
      values  in  the  population.   It  is  described in NM-TRAN using
      ETA(n) variables.  PRED describes the effect of  these  variables
      to  NONMEM via the partial derivatives in the G array.  The vari-
      ance of these variables is given in the OMEGA matrix.

      Random intra-individual variability refers to unexplained (resid-
      ual)  error  in a model (the difference between observed and pre-
      dicted values).  It is  described  in  NM-TRAN  using  EPS(n)  or
      ERR(n) variables. PRED describes the effect of these variables to
      NONMEM via the partial derivatives in the H array.  The  variance
      of these variables is given in the SIGMA matrix.

 Case 2. When the data are single-subject
      Random inter-individual variability refers unexplained (residual)
      error in a model (the difference between observed  and  predicted
      values).  This, despite the fact that data may come from a single
      subject, is because each observation is placed  into  a  separate
      individual  record, and because only level-one random effects are
      needed to describe it.  It is described in NM-TRAN  using  ERR(n)
      or  ETA(n)  variables.   PRED describes the effect of these vari-
      ables to NONMEM via the partial derivatives in the G array.   The
      variance of these variables is given in the OMEGA matrix.

      However,  when  the  data  are in fact from a single subject, and
      when there is no need to use NONMEM terminology, then users often
      associate the ETA(n) and OMEGA with intra-individual variability,
      which corresponds to their experimental point of view.

REFERENCES: Guide I Section A.5, E


  
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