I totally agree with everything you've written, Chris. But let me stick for
a second to actual values of utilities. I am not asking: is this covariate
strong/weak for practical reasons, but rather: which of the 2 is
stronger/weaker.

Now to what Ralph's written: So, the variance is small (within group) would
imply a stronger covariate. Agreed. How about the means? For example, let's
discuss only 1 attribute with 4 levels.

Covariate Scenario 1:
Group 1's beta means are -2, -1, +1, and +2.
Group 2's beta means are +2, +1, -1, and -2.

Covariate Scenario 2:
Group 1's beta means are -4, -2, +2, and +4.
Group 2's beta means are +4, +2, -2, and -4.

Which covariate is stronger?
Dimitri


On Wed, Mar 2, 2011 at 1:07 PM, Wirth, Ralph (GfK SE)
<ralph.wirth@gfk.com>wrote:

> I'd say if the groups that are defined by the covariate are very different
> with regard to their preferences (i.e. utility parameters) and at the same
> time the members of each group are very homogeneous, then the covariate is a
> "strong" covariate.
>
>
>
>
>
>
>
> -----Ursprüngliche Nachricht-----
> Von: r-sig-dcm-bounces@r-project.org [mailto:
> r-sig-dcm-bounces@r-project.org] Im Auftrag von Dimitri Liakhovitski
> Gesendet: Mittwoch, 2. März 2011 19:04
> An: R DCM List
> Betreff: [R-sig-DCM] What is a strong covariate in CBC/HB?
>
> Guys, I could ask some of you individually but it's always better to talk
> to
> several smart guys at a time.
> Some of you know I am working on a project for an ART-Forum which explores
> the issue of covariates in CBC/HB estimation: Is estimation with covariates
> useful?
>
> I have a question: what do YOU THINK is a "strong" covariate? (and let's
> assume we know what the true utilities and their dependence on the
> covariate
> are)
> I am looking less for a mathematical answer (although it's OK if it is) and
> more for a conceptual answer, maybe even with examples. Like: assume we
> have
> a covariate with only 2 levels (i.e., respondents belong to 2 groups): what
> should their preferences be like in order for us to be able to say: group
> membership a strong covariate / weak covariate? And if we have 3 groups?
> Also, I am looking less for a "correct" answer and more for your opinions.
>
> Looking forward to your replies!
>
> Dimitri Liakhovitski
> ninah.com
>
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