imbalanced design? [Software]

posted by Helmut Homepage – Vienna, Austria, 2008-05-06 18:13 (5805 d 12:46 ago) – Posting: # 1822
Views: 20,661

Dear Eva!

One example in SAS…
                  SUM OF
                  SQUARES     MEAN
EFFECT            TYPE I  DF SQUARE  F-VALUE P-VALUE
----------------------------------------------------
TREATMENT           0.956  1   0.956   7.961   0.007
SUBJ. WITHIN SEQ.  17.802 46   0.387   3.224   <.001
PERIOD              0.100  1   0.100   0.835   0.366
SEQUENCE            0.694  1   0.694   1.794   0.187
ERROR               5.521 46   0.120


… and WinNonlin 5.2
Partial Sum of Squares
Hypothesis      DF    SS       MS     F_stat  P_value
-----------------------------------------------------
SEQUENCE         1  0.694182 0.694182 1.79377  0.1870
SEQUENCE*SUBJ.  46 17.8019   0.386997 3.22418  0.0001
TREATMENT        1  0.955579 0.955579 7.9612   0.0070
PERIOD           1  0.100213 0.100213 0.834903 0.3656
Error           46  5.52136  0.12003


Obviously sequence effects are identical (p 0.187). Maybe you had some drop-outs in your study, which resulted in imbalanced sequences. In such a case SAS’ SS Type III and WinNonlin’s Partial Sum of Squares may differ (although they ‘coincide in most situations’). SAS SS III is a strange cup of tea anyhow… ;-)

It would be nice, if you would come up with a simple dataset (12 subjects?), where you find differences. It should be possible to track it down!

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