```Date: Sat, 14 Aug 2010 17:57:13 -0400 Reply-To: R B Sender: "SPSSX(r) Discussion" From: R B Subject: Re: logistic regression interaction In-Reply-To: <1281819852709-2635437.post@n5.nabble.com> Content-Type: text/plain; charset=ISO-8859-1 Anna, To answer your question, we need to write out the equation, and to write out the equation we need to have common language: If you have two categorical independent variables (Factor A has two levels and Factor B has 3 levels), then let A2 be the indicator of Factor A and B2 and B3 be the indicators of Factor B. The first levels of Factor A and B are the reference groups. Lower case letters denote coefficients. Equation: logit(y) = m + a2*A2 + b2*B2 + b3*B3 + ab22*A2*B2 + ab23*A2*B3 Then, Odds|(A=1,B=1) = exp(m) Odds|(A=1,B=2) = exp(m + b2) Odds|(A=1,B=3) = exp(m + b3) Odds|(A=2,B=2) = exp(m + a2 + b2 + ab22) Odds|(A=2,B=3) = exp(m + a2 + b3 + ab23) Ryan On Sat, Aug 14, 2010 at 5:04 PM, annastella wrote: > Hi Ryan, > > Thanks a lot for that-will have a go with it and see what it gives me. > > However, may I ask if you or anyone knows a way to calculate the odds ratios > (not the CIs necessarily) for the categories missing in the output (i.e. 3 > social class groups for non shift-workers)? Not in terms of syntax really, > just want to see I understand the interaction calculation right while > working this out. > > Many thanks > Anna > -- > View this message in context: http://spssx-discussion.1045642.n5.nabble.com/logistic-regression-interaction-tp2635146p2635437.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 > ===================== 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 ```

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