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ROBUST POOLED STANDARD DEVIATIONName:
Let w1, w2, ... , wp be the standard deviations from the p labs. The degrees of freedom for wi = ni - 1 where ni is the number of replications for lab i.
Compute the limit factor,
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with
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with
The limit factor and adjustment factor assume that each lab has the same number of replications. If the number of replications are not equal, Dataplot will use the average number of replications. The initual value of w* is set to the median of the wi's. To update the value of w* compute
![]() For each wi,
![]() The updated value of w* is
![]() The value of w* is iterated until the difference between two successive values of w* is sufficiently small.
The ISO 13528 standard also allows this computation to be performed
on the lab ranges. In this case, the robust pooled range uses the
same computation as above with the exception that the degrees of
freedom,
<SUBSET/EXCEPT/FOR qualification> where <y> is the response variable; <x> is the lab-id variable; <par> is a parameter where the computed robust pooled sd is saved; and where the <SUBSET/EXCEPT/FOR qualification> is optional.
<SUBSET/EXCEPT/FOR qualification> where <y> is the response variable; <x> is the lab-id variable; <par> is a parameter where the computed robust pooled range is saved; and where the <SUBSET/EXCEPT/FOR qualification> is optional.
LET SD = ROBUST POOLED STANDARD DEVIATION Y X SUBSET TAG > 2 LET SD = ROBUST POOLED RANGE Y X
SKIP 25 READ GEAR.DAT Y X . SET LET CROSS TABULATE COLLAPSE LET YSD = CROSS TABULATE SD Y X LET NSIZE = CROSS TABULATE SIZE X LET NREPL = MEAN NSIZE . LET A = ROBUST POOLED STANDARD DEVIATION YSDThe returned value is 0.5335508E-02.
Date created: 01/06/2011 |