Date:         Fri, 3 Jun 2005 06:30:43 -0400
Reply-To:     Peter Flom <flom@NDRI.ORG>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         Peter Flom <flom@NDRI.ORG>
Subject:      Re: trend test
Content-Type: text/plain; charset=US-ASCII

I missed the original post, and only saw David Cassell's response, where
(as usual) he offered excellent advice.  I add my thoughts at the end


"'rique" <kique105@yahoo.com> wrote:
<<<<
I have race distribution (W,B,H) by year (2000-2003) and I want to test
whether there is any trending (increasing or decreasing) WITHIN each
race group. In other words, for Hispanics, is the population
significantly increasing or decreasing by year. I know there is a CHISQ
test for trend, but I don't know how to set it up. I know there is a
significant difference in race distribution BETWEEN groups, but that's
not what I want. Can anyone help me with this?
>>>>

David replied

<<<<
I'm sure someone on SAS-L can help you.  But I think you're going to
have to give us more information before we can help.
You say you have "race distribution (W,B,H) by year (2000-2003)".  What
does that mean?

Do you have some percents in a 3x4 table?  If that's what you have, then
you're not going to be able to perform a chi-squared test in PROC FREQ.
And if you only have a 3x4 table, then you're not going to have many
degrees of freedom for whatever test you want.  Fewer degrees of freedom
makes it that much harder to establish a statistically valid effect.

When you plot your data, do you see trends for each separate race class?
If not, then this could be a problem in your analysis.  Do they all go
in the same direction?  If not, then you'll have interaction terms which
have to be dealt with.

So perhaps you could write back to SAS-L (not to me personally) and
explain more about your data and your goals.  Then we can give you some
better advice.
>>>

I *THINK* that he has a 3x4 table  In each row, he has 4 %s (what these
are isn't clear - but maybe it's % of people who have or do something).
So, if he wants a test for trend WITHIN race, he could turn it into 4
2x4 tables, each with ONE race, and the rows being "yes" and "no" or
whatever, and then do a test for trend, or (my preference) a Jonckheere
Terpstra test
for each table.

Of course, I am operating somewhat blind here, given the lack of
information, and may be all wrong.

Peter

Peter L. Flom, PhD
Assistant Director, Statistics and Data Analysis Core
Center for Drug Use and HIV Research
National Development and Research Institutes
71 W. 23rd St
www.peterflom.com
New York, NY 10010
(212) 845-4485 (voice)
(917) 438-0894 (fax)