Logistic Regression - Threshold effect sizes?

[Jon Bernard-2]

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
[hidden email] (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

[SR Millis-3]

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:  [hidden email]
Tel: [phone]
Fax: [phone]


--- On Fri, 9/5/08, Jon Bernard <[hidden email]> wrote:

> From: Jon Bernard <[hidden email]>
> Subject: Logistic Regression - Threshold effect sizes?
> To: [hidden email]
> 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
> [hidden email] (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
[hidden email] (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

[Jon Bernard-2]

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 <[hidden email]> 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:  [hidden email]
> Tel: [phone]
> Fax: [phone]
>
>
> --- On Fri, 9/5/08, Jon Bernard <[hidden email]> wrote:
>
> > From: Jon Bernard <[hidden email]>
> > Subject: Logistic Regression - Threshold effect sizes?
> > To: [hidden email]
> > 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
> > [hidden email] (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
[hidden email] (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