Just to add a little bit to what David M. says:
(1) The promax oblique rotation starts out with a varimax rotated
orthogonal loadings matrix which it then attempts to convert this
into a correlated matrix .The SPSS algorithms page goes through
the steps here:
http://pic.dhe.ibm.com/infocenter/spssstat/v20r0m0/index.jsp?topic=%2Fcom.ibm.spss.statistics.help%2Falg_factor_promax.htmQuoting from the page:
The rotated factor pattern is
Λpromax=ΛvarimaxQC−1
In the Varimax solution, the loadings for items 23 and 24 are
positive and remain positive after the transformation to promax
(see the varimax output on the UCLA website).
(2) I believe that the oblimin rotation starts out with original
unrotated (orthogonal) factor matrix and on the UCLA website,
items 23 and 24 have negative loadings on the third factor. The
mathematical steps that are involved in doing the oblimin rotation
are given on the SPSS algorithms page but some may find the
math opaque; see:
http://pic.dhe.ibm.com/infocenter/spssstat/v20r0m0/index.jsp?topic=%2Fcom.ibm.spss.statistics.help%2Falg_factor_oblique.htmThis point of view is consistent with presentations on the differences
between promax and direct oblimin methods; see (esp p435):
http://books.google.com/books?hl=en&lr=&id=-VTvN3aPw8sC&oi=fnd&pg=PA424&dq=%22promax+rotation%22+%22factor+analysis%22+%22bipolar+factor%22&ots=Fwr4FO9wUF&sig=f457lVvVf6u76QqYJn0zkHOVD0I#v=onepage&q=oblimin&f=falseI believe that in the present case, the oblimin transformation
maintains the sign of the original loadings on the third factor though
why this is true is not clear to me. While David says that the sign is
unimportant I do believe that most analysts would be confused by
difference in signs. Also, many report that both promax and oblimin
give similar results which one can argue is not the strictly true here.
It is possible that someone has studied the conditions under which
the signs of the loadings given by promax and oblimin are different
but I'm not aware of them.
-Mike Palij
New York University
[hidden email].
----- Original Message -----
From: "David Marso" <
[hidden email]>
To: <
[hidden email]>
Sent: Saturday, November 09, 2013 1:23 AM
Subject: Re: Positive loadings with PROMAX, negative with OBLIMIN
> Bruce,
> Plot the loadings in a 3-d scatterplot. The 3rd factor of the
> oblimin is
> simply 180 degrees (flipped) from the promax. Sign of the loadings is
> not
> of importance WRT interpretation. Do a simple scatter of the two
> solutions
> (3rd factor) and they are practically on a straight line (negative
> slope).
> I OMS'd the factor and structure matrices and played around but the
> battery
> on my LT fizzled before I could wrangle the output.
> I'll leave it to OP Bruce to drill down into that (best turn off the
> blank
> (.30) to explore this). Now, IBM (I guess Jon *Why isn't the pattern
> matrix
> available in the OMS tags? Oversight?*
> - BTW, why are you the only IBMer that posts here with any regularity?
> Back
> in the day a lot of SPSS staff participated. The only person recently
> was D
> Dwyer who looked into my MATRIX issue (where are D.Nich.... and
> D.Math...).
> Oh well, I guess IBM doesn't give a hoot about SPSSX-L -aside from you
> Jon)
> Squeak!
> HTH, David
>
> Art Kendall wrote
>> In any case, there is no intrinsic meaning to the direction that
>> the artificial dimension takes. E.g., for one set of
>> cases
>> to
>> another the signs may all be flipped.
>>
>>
>> Art Kendall
>> Social Research Consultants
>> On 11/8/2013 5:45 PM, Bruce Weaver [via SPSSX Discussion]
>> wrote:
>>
>> Here's another little factor analysis mystery I
>> stumbled across. I'm using the data file available on
>> this
>> UCLA
>> webpage:
>>
http://www.ats.ucla.edu/stat/spss/output/factor1.htm>> .
>> Here's my syntax, with my question at the end.
>>
>>
>>
>> NEW FILE.
>>
>> DATASET CLOSE all.
>>
>>
>> GET FILE='C:\bw\SPSS\data\UCLA\M255.SAV'.
>>
>>
>> DESCRIPTIVES item13 to item24.
>>
>>
>> factor
>>
>> /variables item13 to item24
>>
>> /print initial extraction rotation fscore
>>
>> /format blank(.30)
>>
>> /criteria factors(3) iterate(100)
>>
>> /extraction paf
>>
>> /rotation promax
>>
>> /method = correlation.
>>
>>
>> * Factor 3 loadings (from Pattern Matrix) are: 0.781 and
>> 0.821.
>>
>> * This matches results shown in one analysis on the UCLA
>> web-page.
>>
>>
>> factor
>>
>> /variables item13 to item24
>>
>> /print initial extraction rotation fscore
>>
>> /format blank(.30)
>>
>> /criteria factors(3) iterate(100)
>>
>> /extraction paf
>>
>> /rotation oblimin
>>
>> /method = correlation.
>>
>>
>> * Factor 3 loadings (from Pattern Matrix) are: -0.778 and
>> -0.814.
>>
>>
>> * Q. Why does the sign change when I switch from PROMAX to
>> OBLIMIN? .
>>
>>
>>
>> My apologies to the EFA experts out there if this is a
>> well-known
>> phenomenon. (I'm a bit of a duffer when it comes to
>> multivariate
>> stuff, including EFA!)
>>
>>
>> Cheers,
>>
>> Bruce
>>
>>
>> --
>>
>> Bruce Weaver
>>
>>
>
>> bweaver@
>
>>
>>
>>
http://sites.google.com/a/lakeheadu.ca/bweaver/>>
>> "When all else fails, RTFM."
>>
>>
>> NOTE: My Hotmail account is not monitored regularly.
>>
>> To send me an e-mail, please use the address shown above.
>>
>>
>>
>>
>>
>>
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>
>
>
>
>
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