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Second, exchanges on the statalist have suggested that the confidence intervals calculated by nlcom may not be the what I want: http://www.stata.com/statalist/archive/2011-12/msg00389.html I would be grateful to hear recommendations regarding how to calculate the odds ratios I want. Is the approach in the code below okay? Should I use the margins command instead? When I have seen people use the margins command to get odds and then calculate odds ratios, they have been working with interactions between dummy variables and logistic regression. For example: http://www.stata.com/statalist/archive/2011-05/msg00776.html I am not sure how to use margins with a dummy X continuous interaction and a mlogit model where I must specify which outcome I want. The use of expression(exp(xb())) for getting the odds seems to preclude the use of the predict() option that is used to specify which outcome to use. Thanks, Jeremy ****************** *mlogit with binary by continuous interaction *slightly modified from example posted at http://www.stata.com/statalist/archive/2010-10/msg00149.html ***************** sysuse auto, clear // create an indicator variable that is // 1 when an observation has valid values // on mpg, price, and rep78, and 0 otherwise gen byte touse = !missing(mpg, price, rep78) // center mpg sum mpg if touse, meanonly gen c_mpg = mpg - r(mean) // center price and change unit to 1000s of $ sum price if touse, meanonly *recode price so cheapest car =0 gen c_price = (price - r(min))/1000 // I have changed this line to subtract the min rather than the mean sum c_price // see the example FAQ recode rep78 1/2 = 3 gen byte baseline = 1 // add value labels to rep78 label define rep78 3 "Average" /// 4 "Good" /// 5 "Excellent" label value rep78 rep78 // the model mlogit rep78 foreign##c.c_price c_mpg baseline, rrr nocons // the original post had an interaction between c_mpg and c_price *calculate odds ratio for foreign (outcome=Good) with 1,000-9,000 increases in price sum c_price if e(sample) foreach x of numlist 1/9 { di "Odds Ratio for foreign with a `x' thousand dollar increase in price." nlcom exp(_b[Good:1.foreign])*exp(_b[Good:1.foreign#c.c_price])^`x' - 1 } -- ******************** Dr. Jeremy Reynolds Associate Professor Undergraduate Coordinator Department of Sociology 117 Baldwin Hall University of Georgia Athens, GA 30602-1611 Phone: (706) 583-8072 Web: http://uga.edu/soc/people/faculty/reynolds_jeremy.php Fax: (706) 542-4320 * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/faqs/resources/statalist-faq/ * http://www.ats.ucla.edu/stat/stata/

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