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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  (resi-
      dual)  error  in  a  model  (the  difference between observed and
      predicted 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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