LISTSERV at the University of Georgia
Menubar Imagemap
Home Browse Manage Request Manuals Register
Previous messageNext messagePrevious in topicNext in topicPrevious by same authorNext by same authorPrevious page (May 2006)Back to main SPSSX-L pageJoin or leave SPSSX-L (or change settings)ReplyPost a new messageSearchProportional fontNon-proportional font
Date:         Tue, 16 May 2006 13:22:53 -0400
Reply-To:     "Thompson, Carol" <CThompson@anteon.com>
Sender:       "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From:         "Thompson, Carol" <CThompson@anteon.com>
Subject:      Re: CHAID with small sample
Content-Type: text/plain; charset="us-ascii"

Hector,

My error for not indicating that the test for determining split levels is based on the measurement type of the dependent variable -- nominal, ordinal or continuous. I had my work in mind. Thanks for bringing up the clarification. Our feedback, however, is the same -- sample size makes a difference.

Thanks,

Carol

Carol B. Thompson Sr. Programmer/Analyst Anteon Corporation 181 N. Arroyo Grande Blvd, Ste 105 Henderson, NV 89074-1624 Ph: (702) 731-5550 x 111 Fax: (702) 731-4027

-----Original Message----- From: SPSSX(r) Discussion [mailto:SPSSX-L@LISTSERV.UGA.EDU] On Behalf Of Hector Maletta Sent: Tuesday, May 16, 2006 10:07 AM To: SPSSX-L@LISTSERV.UGA.EDU Subject: Re: CHAID with small sample

Chaid is based on chi square, and therefore the number of cases and the number of categories involved IN EACH LEVEL is important for the significance of results. If a simple chi square test fails with your sample, then Chaid will give you non significant results. Hector

-----Mensaje original----- De: SPSSX(r) Discussion [mailto:SPSSX-L@LISTSERV.UGA.EDU] En nombre de Thompson, Carol Enviado el: Tuesday, May 16, 2006 1:28 PM Para: SPSSX-L@LISTSERV.UGA.EDU Asunto: Re: CHAID with small sample

Nico,

When I worked with CHAID and CART a few years ago with about 100-150 cases, I ended up feeling like I was reaching ---- and we were just looking for major predictors not a precise prediction tool. Remember that at each split level, CHAID is attempting to determine a splitting predictor and the groupings of that predictor's categories that have the largest between group differences (via an F-test like with a one-way anova). With 35 cases, you "might" find a top-level split predictor if there are big differences between categories. Because CHAID helps identify localized, rather than globalized, interactions via sequential partitioning, each subgroup goes through the same process of looking at potentially good splitting predictors. Since each subgroup will have less cases than the original group of 35, further splits will only occur if there are very big differences between the group categories. You certainly can run the CHAID procedure as an exploratory tool to see what happens (even with a higher alpha of 0.10); however, I would suggest being careful about how you use any results. With such a small sample you have no data for validating any resulting model. I'm not aware of an Exact Test option for CHAID.

Hope that helps.

Carol

Carol B. Thompson Sr. Programmer/Analyst Anteon Corporation 181 N. Arroyo Grande Blvd, Ste 105 Henderson, NV 89074-1624 Ph: (702) 731-5550 x 111 Fax: (702) 731-4027

-----Original Message----- From: SPSSX(r) Discussion [mailto:SPSSX-L@LISTSERV.UGA.EDU] On Behalf Of Nico Peruzzi Sent: Friday, May 12, 2006 6:57 AM To: SPSSX-L@LISTSERV.UGA.EDU Subject: CHAID with small sample

Has anyone had experience doing CHAID with a small sample size N = about 35. Not worth it? Better to use Exact Tests? My client is reaching for some way to milk this small bit of data. The data fits for CHAID, as do the questions, but it's just such a small amount. Is there an exact test option in CHAID?

Thanks, Nico

-- Nico Peruzzi, Ph.D.


Back to: Top of message | Previous page | Main SPSSX-L page