Bookmark and Share

Notice: On April 23, 2014, Statalist moved from an email list to a forum, based at statalist.org.


[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: st: Interactions in xreg


From   Morten Hesse <[email protected]>
To   [email protected]
Subject   Re: st: Interactions in xreg
Date   Mon, 23 Aug 2010 13:06:21 +0200


Den 23-08-2010 12:33, Maarten buis skrev:
--- On Mon, 23/8/10, Morten Hesse wrote:
I did that too, and it works. "Block" is of course an
ordinal variable (1-5). Yet, I want to test whether
the group with characteristic "ant" has a different
pattern of behaviour over "blocks", and I have reasons
to believe that that pattern is curvilinear, compared
with subjects who do net have characteristic "ant"
(scores increases towards the middle, of the test,
decreases towards the end). I can of course test
whether the parameter for subjects during the
different blocks are significant (e.g., start versus
middle, and middle  versus start). And indeed, they
are. But I have never seen that used as  a test of
curvilinearity, and I feel that it is a bit "informal".
Am I wrong?
Yes, unfortunately you are wrong. Such quadratic terms
have no meaning in an ordinal variable. If you do so
you are basically assuming that the distances between
your 5 categories are equal.

-- Maarten

--------------------------
Maarten L. Buis
Institut fuer Soziologie
Universitaet Tuebingen
Wilhelmstrasse 36
72074 Tuebingen
Germany

http://www.maartenbuis.nl
--------------------------




*
*   For searches and help try:
*   http://www.stata.com/help.cgi?search
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/
*
*   For searches and help try:
*   http://www.stata.com/help.cgi?search
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/


© Copyright 1996–2018 StataCorp LLC   |   Terms of use   |   Privacy   |   Contact us   |   Site index