Stephen Brand

www.statisticsdoc.com

Marnie,

Since the interaction was significant, you need not employ an alpha adjustment when you carry out the regressions separately by group.

BTW, it is entirely possible that when you carry out the regressions separately by group, the regression weights will not be significantly different from zero (say if the weight is slightly positive in one group and slightly negative in another group). The interaction test indicates that these weights are significantly different from one another, and this is still the case even if the weights are not significantly different from zero when you carry out regressions by group.

HTH,

Stephen Brand

---- Marnie LaNoue <

[hidden email]> wrote:

> Hi All --

> Any comments appreciated. I tested a regression model with a categorical

> variable to test for differences across groups. The interaction was

> significant, so I ran the separate models for the groups and now want to

> compare the significance of the difference of the betas using t-tests.

> THere are two continuous predictors. Do I need to use an alpha adjustment?

> And, do I need to do it 2 times for the difference in the 2 predictors

> across the 2 groups? Is there an omnibus test that will get me the answer I

> desire?

> Thanks!

> Marnie LaNoue, Ph.D.

> University of New Mexico

--

For personalized and experienced consulting in statistics and research design, visit www.statisticsdoc.com