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From |
Steve Samuels <sjsamuels@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: Stata vs SAS Survey Risk Ratios |

Date |
Thu, 4 Apr 2013 13:50:52 -0400 |

No survey command in Stata uses maximum likelihood, but many solve pseudo-likelihood equations. -svy: glm- with family(binomial) link(log) options would give risk ratios directly, but convergence is sometimes difficult. I would use -svy: logistic- myself: *************CODE BEGINS************* sysuse auto, clear recode rep78 1/2=5 svyset _n svy: logistic foreign turn i.rep78 margins rep78, coeflegend post /* RR 4 vs 3 */ nlcom _b[4.rep78]/_b[3bn.rep78] /* RR 5 vs 3 */ nlcom _b[5.rep78]/_b[3bn.rep78] /* Notice Lower limits above <0. This happens because -nlcom- uses the delta method, which doesn't know about the boundaries. Try again using knowledge that RR>0 */ capture program drop _all program antilog local bound invnorm(.975)*r(se) local lparm r(estimate) local ll exp(`lparm' - `bound') local ul exp( `lparm' + `bound') di _col(1) "parm = " %8.4g exp(`lparm') /// _col(20) "ll =" %8.4g `ll' /// _col(40) "ul =" %8.4g `ul' end svy: logistic foreign turn i.rep78 margins rep78, expression(log(predict(pr))) post /* RR 4 vs 3 */ qui lincom _b[4.rep78]-_b[3bn.rep78] antilog /* RR 5 vs 3 */ qui lincom _b[5.rep78]-_b[3bn.rep78] antilog *****************CODE ENDS ************** On Apr 4, 2013, at 10:48 AM, Joshua Josephs wrote: Dear StataListers, Im trying to find out exactly what Stata does compared to SAS in calculating risk ratios from survey data. In SAS you calculate a survey logistic regression and then use average predicted margins to get the risk ratios. In Stata you use the svy glm command which uses maximum likelihood. Im trying to find out if Statas method provides the appropriate estimates and confidence intervals. Any help is appreciated, Joshua Josephs * * 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/ * * 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/

**References**:**st: Stata vs SAS Survey Risk Ratios***From:*"Joshua Josephs" <backpacker24@excite.com>

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