Simon - slmartys@gmail.com wrote: > > My analysis involves a Generalized Estimating Equation --- two binary IVs > predicting a binary DV. Each binary IV is dummy coded 0-1. > > When I run my analyses, the "test of model effects" Wald chi-square > statistic is exactly the same as the "parameter estimate" Wald chi-square > statistic for each predictor. However, when I add an INTERACTION term to > the model (i.e. I ask SPSS to add it in automatically), this is no longer > the case. (The Wald statistic for the interaction term matches, but the > statistics for the other parameter estimates don't match the test of model > effects.) > > To date, I'm not really clear on why adding the interaction makes this > happen. I would like to report parameter estimates (odds ratios), but the > significance levels of the parameter estimates change depending on which > group I select for the reference group! (Just to reiterate, this does not > happen when there is no interaction term.) > > Is there a way I can code my data so that this does not occur? > > If there's not, what is the appropriate thing to report? > > --- snip --- > >

Bear in mind that when the product term is included in the model, the parameters for the main effects are really giving you simple main effects . Suppose your variables are called A and B. When A*B is also in the model, the parameter for A gives you the effect of A when B is set to its reference level; and the parameter for B gives you the effect of B when A is set to its reference level. So if you change the reference levels, you'll see different parameter estimates. The parameter estimate for the A*B product is unaffected by what you choose as the reference categories.

HTH.

----- -- Bruce Weaver bweaver@lakeheadu.ca http://sites.google.com/a/lakeheadu.ca/bweaver/

"When all else fails, RTFM."

NOTE: My Hotmail account is not monitored regularly. To send me an e-mail, please use the address shown above.

-- View this message in context: http://spssx-discussion.1045642.n5.nabble.com/Parameter-Sig-vs-Effect-Sig-Interaction-tp2845146p2845219.html Sent from the SPSSX Discussion mailing list archive at Nabble.com.

===================== 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