From: nichols@spss.com (David Nichols)
Subject: Re: MANOVA nested design question
Organization: SPSS Inc.
Date: Tue, 29 Sep 1992 22:35:03 GMT


R. Wytek writes:

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My responses are inside the dotted lines, like this.
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A student here has data sampled at 5 different 'locations' and nested
under the locations a varying number of 'clutches', i.e. 2 to 6.

Now she did 2 different MANOVAs, only one giving results, the other
giving syntax errors.

My questions are:  1.) are the two forms really equivalent?
                       I don't think so but until now we found
                       only the first form operable.

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No, they are not equivalent. The first one tells MANOVA to fit the effect
of CLUTCH separately within each level of LOC and then pool these 
together in a single test. The second is trying (I assume) to look at
individual degree of freedom effects of CLUTCH within LOC. Note in both
cases that if the design is unbalanced, use of one term or subset of a
term on the DESIGN, without including the other effects in the model
gives different results than including them. In particular, neither of
these is appropriate when testing simple effects in unbalanced data.
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                   2.) why is the second form not possible?

1st form:    MANOVA   list of dep vars  BY LOC(1,5) CLUTCH(2,6)/
                      PRINT= cell(means) homo(all) signif(univ averf)/
                      DESIGN= CLUTCH WITHIN LOC

2nd form:    MANOVA   list of dep vars  BY LOC(1,5) CLUTCH(2,6)/
                      PRINT= ...as above.../
                      PARTITION (CLUTCH) = (5,4,2,5) /
                      DESIGN= CLUTCH(1) within LOC(1)
                              CLUTCH(2) within LOC(2)
                              CLUTCH(3) within LOC(3)
                              CLUTCH(4) within LOC(4)

             this form works only for a maximum of two WITHINs in
             the DESIGN command, why?

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The problem is that the PARTITION subcommand requests a total of 16 degrees
of freedom for an effect that has only five df. The syntax for PARTITION
should include a listing of numbers that do not sum to more than the df
available for the CLUTCH factor. In this case, what happens is that the
first partition gets all the df since the number is larger than the total
available df, and there isn't anything left for the other terms. The
error message given isn't very helpful, and the parser should have been
set up to take care of this. As mentioned below, it will in the future.
If you don't understand what happened, try running it with the same syntax,
except ask only for two pieces of the effect. You'll still get an error
message, because it is still trying to fit two partitions when only one
exists. If you change the first number in parentheses to a 1 and run it
asking for two partitions on the DESIGN you'll see a 1 df test, followed
by the remaining 3 df in a second piece.
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I hope someone can give us some hints and even more I hope I will
see before retiring a better documentation of procedure MANOVA,
the present one is of questionable value for non-specialists.

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As a matter of fact, I spent a great deal of time recently reviewing the
syntax descriptions in the MANOVA chapters, and I think that the documentation
will be improved for version 5. We made quite a few changes, thought the 
basic structure is still the same. However, the problem here is not with
the documentation. As is clearly stated on p. 371 of the SPSS Reference
Guide accompanying release 4 on mainframe, or p. C-47 of the SPSS/PC+
Advanced Statistics 4.0 Guide, "Each value in the partition list must be a
positive integer and the sum of the values cannot exceed the degrees of
freedom for the factor."

The parsing and failure to issue an appropriate error message is a problem
that clearly contributed to the confusion though. If you try this same
syntax in version 5 (the next thing out) you would get the following error
message:

>The vector specified in the PARTITION subcommand is incorrect.  The values
>must be positive integers, and must not total more than the number of degrees
>of freedom in the factor variable.
>This command not executed.

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--
 David Nichols           Statistical Support Specialist            SPSS, Inc.
 Phone: (312) 329-3684     Internet: nichols@spss.com     Fax: (312) 329-3657
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 Any correlation between my views and those of SPSS is strictly due to chance.