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Date:         Tue, 9 Sep 2008 15:57:16 -0400
Reply-To:     Jon Bernard <jon563@gmail.com>
Sender:       "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From:         Jon Bernard <jon563@gmail.com>
Subject:      Re: Fw: Re: Logistic Regression - Threshold effect sizes?
Comments: To: SR Millis <srmillis@yahoo.com>
In-Reply-To:  <282107.24621.qm@web50908.mail.re2.yahoo.com>
Content-Type: text/plain; charset=ISO-8859-1

Thanks again Scott.

I tried this method and now have to make sense of the output. I entered one ordinal covariate and one binary DV, selecting the option for contrasts as you explained below.

The results give the following Exp(B)'s (all of them significant at p < .001): var1(1) = 2.704 var1(2) = 2.198 var1(3) = 1.649 var1(4) = 1.189

Could I interpret this as suggesting that the impact of a one-point positive change in response to the item is greater when the baseline value is 1 than when it is 2, 3, or 4?

Thank you,

Jon

On Fri, Sep 5, 2008 at 6:36 PM, SR Millis <srmillis@yahoo.com> wrote:

> Jon, > > If you're using SPSS binary logistic regression, enter your ordinal > variable as a covariate. Then, click on the Categorical button. This will > take you to a new window where you indicate which covariates are > categorical. The Contrast should be "Indicator." Then run the analysis. > > If you're using Stata software, you use the xi option. > > Scott Millis > > > > > --- On Fri, 9/5/08, Jon Bernard <jon563@gmail.com> wrote: > > > From: Jon Bernard <jon563@gmail.com> > > Subject: Re: Fw: Re: Logistic Regression - Threshold effect sizes? > > To: "SR Millis" <srmillis@yahoo.com> > > Cc: SPSSX-L@listserv.uga.edu > > Date: Friday, September 5, 2008, 6:24 PM > > Thank you Scott. Would you recommend any resources for a > > quick study on > > this technique? > > > > Jon > > > > On Fri, Sep 5, 2008 at 6:18 PM, SR Millis > > <srmillis@yahoo.com> wrote: > > > > > Jon, > > > > > > If you're uncomfortable treating your ordinal > > variable > > > as though it were interval, you can always "dummy > > > code" the ordinal variable---such that the > > 5-category > > > variable become 4 separate variables---and direct > > > comparisons can be made. This can work pretty well if > > you > > > don't have a lot of ordinal vairables and if > > you're > > > sample size is sufficiently large. > > > > > > Scott Millis > > > > > > > --- On Fri, 9/5/08, Justin Black > > > > <justin.black@gmail.com> wrote: > > > > > > > > > From: Justin Black > > <justin.black@gmail.com> > > > > > Subject: Re: Logistic Regression - Threshold > > effect > > > > sizes? > > > > > To: "SR Millis" > > <srmillis@yahoo.com> > > > > > Date: Friday, September 5, 2008, 6:13 PM > > > > > Scott, thank you for following up. > > > > > > > > > > What's puzzling to me is the seemingly > > omnibus > > > > nature > > > > > of the effect. So, I > > > > > could say that a 1-point increase in IV1 is > > associated > > > > with > > > > > a, e.g., 40% > > > > > increase in the likelihood of the event > > occurring. > > > > But > > > > > that assumes that a > > > > > 1-point increase in the IV has the same > > effect on the > > > > DV > > > > > regardless of the > > > > > baseline level of the IV. I don't think > > that > > > > > assumption is accurate in > > > > > these particular data. > > > > > > > > > > I really feel like I'm missing something > > here, > > > > just > > > > > can't figure out what. > > > > > A look back at Hosmer & Lemeshow > > didn't help > > > > any. > > > > > > > > > > Thank you, > > > > > > > > > > Jon > > > > > > > > > > On Fri, Sep 5, 2008 at 6:00 PM, SR Millis > > > > > <srmillis@yahoo.com> wrote: > > > > > > > > > > > Jon, > > > > > > > > > > > > What is puzzling in the results? > > > > > > > > > > > > Have you examined the degree of > > collinearity > > > > among the > > > > > > predictors/covariates? > > > > > > > > > > > > > > > > > > > > > > > > Scott R Millis, PhD, MEd, ABPP > > (CN,CL,RP), CStat > > > > > > Professor & Director of Research > > > > > > Dept of Physical Medicine & > > Rehabilitation > > > > > > Wayne State University School of > > Medicine > > > > > > 261 Mack Blvd > > > > > > Detroit, MI 48201 > > > > > > Email: smillis@med.wayne.edu > > > > > > Tel: 313-993-8085 > > > > > > Fax: 313-966-7682 > > > > > > > > > > > > > > > > > > --- On Fri, 9/5/08, Jon Bernard > > > > > <jon563@gmail.com> wrote: > > > > > > > > > > > > > From: Jon Bernard > > <jon563@gmail.com> > > > > > > > Subject: Logistic Regression - > > Threshold > > > > effect > > > > > sizes? > > > > > > > To: SPSSX-L@LISTSERV.UGA.EDU > > > > > > > Date: Friday, September 5, 2008, > > 5:42 PM > > > > > > > Fellow SPSSers, > > > > > > > > > > > > > > I am struggling with a logistic > > regression > > > > issue > > > > > and > > > > > > > thought I'd put it out > > > > > > > to the list for some clarity. > > > > > > > > > > > > > > The dependent variable of interest > > is a > > > > binary > > > > > event (0 = > > > > > > > Did not happen, 1 > > > > > > > = Did happen). The independent > > variables of > > > > > interest are > > > > > > > ordinal > > > > > > > attitudinal survey items, with > > responses on > > > > a > > > > > 5-point scale > > > > > > > (1 = Strongly > > > > > > > Disagree, 5 = Strongly Agree). I > > have been > > > > using > > > > > logistic > > > > > > > regression for > > > > > > > the analysis, but either I'm > > missing > > > > > something in the > > > > > > > results output or I'm > > > > > > > using the wrong statistical > > technique. I > > > > have an > > > > > inkling > > > > > > > that the intervals > > > > > > > between categories of the > > independent > > > > variables > > > > > are not all > > > > > > > equal. In other > > > > > > > words, I think that the impact on > > the > > > > dependent > > > > > variable of > > > > > > > an independent > > > > > > > variable score of 3 vs. one of 2 > > is greater > > > > than > > > > > that of a > > > > > > > score of 5 vs. > > > > > > > one of 4. Is that clear? If so, > > what would > > > > you > > > > > recommend > > > > > > > in order to test > > > > > > > that hypothesis? Is there a class > > of > > > > techniques > > > > > designed > > > > > > > particularly for > > > > > > > this kind of test? > > > > > > > > > > > > > > Very many thanks in advance for > > your > > > > assistance > > > > > with this > > > > > > > matter. > > > > > > > > > > > > > > Kind regards, > > > > > > > > > > > > > > Jon > > > > > > > > > > > > > > ===================== > > > > > > > To manage your subscription to > > SPSSX-L, send > > > > a > > > > > message to > > > > > > > LISTSERV@LISTSERV.UGA.EDU (not to > > SPSSX-L), > > > > with > > > > > no body > > > > > > > text except the > > > > > > > command. To leave the list, send > > the command > > > > > > > SIGNOFF SPSSX-L > > > > > > > For a list of commands to manage > > > > subscriptions, > > > > > send the > > > > > > > command > > > > > > > INFO REFCARD > > > > > > > > > > > > ===================== > > > To manage your subscription to SPSSX-L, send a message > > to > > > LISTSERV@LISTSERV.UGA.EDU (not to SPSSX-L), with no > > body text except the > > > command. To leave the list, send the command > > > SIGNOFF SPSSX-L > > > For a list of commands to manage subscriptions, send > > the command > > > INFO REFCARD > > > >

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