Date:         Wed, 25 Jun 2003 14:39:57 -0400
Reply-To:     Christina Cutshaw <ccutsha1@jhem.jhmi.edu>
Sender:       "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From:         Christina Cutshaw <ccutsha1@jhem.jhmi.edu>
Subject:      Interaction term significant but sub-group p-value is not
Content-Type: text/plain; charset=us-ascii

List Members,

Does anyone know why one would have a significant interaction term but
the odds ratios of the specific subgroup is not significant?

I have two variables: affiliation (3 nominal groups A, B, C) and staff
(0=0, 1=>0).
In my binary logistic model I ran: affiliation, staff, and an
interaction term affiliation*staff.

In my output I have:

Affiliation B (1) ignore
Affiliation C (2) ignore
Staff (1) use info for affiliation reference group A
Affiliation B(1)*staff (1) p=0.101 (ignore OR, etc.)
Affiliation C( 2)*staff (1) p=0.020 (ignore OR etc.)

The odds ratio, CI and p-value of staff (1) the Affiliation (2) group is
OR=4.50, 95% CI=0.89, 22.64, p=0.068

Why would the interaction term be significant at p=0.020 but the p-value
for the actual group is 0.068?

Thanks!

Chris Cutshaw