topic Re: proc genmod SE doesn't match proc ttest SE in SAS Programming https://communities.sas.com/t5/SAS-Programming/proc-genmod-SE-doesn-t-match-proc-ttest-SE/m-p/734237#M228761 I guess the distribution is different . T distribution V.S. Normal distribution. Thu, 15 Apr 2021 12:40:13 GMT Ksharp 2021-04-15T12:40:13Z proc genmod SE doesn't match proc ttest SE https://communities.sas.com/t5/SAS-Programming/proc-genmod-SE-doesn-t-match-proc-ttest-SE/m-p/734016#M228715 <P>What is the difference between how standard error is calculated in proc ttest vs. proc genmod dist=normal.</P><P>I ran the following codes:</P><UL><LI>proc ttest; class group; var age; run;</LI><LI>proc genmod; class group; model age=group / dist=normal; lsmeans group; run;</LI></UL><P>The same means were produced but the standard errors were different.&nbsp; Anyone know why?</P><P>&nbsp;</P> Thu, 15 Apr 2021 02:06:10 GMT https://communities.sas.com/t5/SAS-Programming/proc-genmod-SE-doesn-t-match-proc-ttest-SE/m-p/734016#M228715 best_means 2021-04-15T02:06:10Z Re: proc genmod SE doesn't match proc ttest SE https://communities.sas.com/t5/SAS-Programming/proc-genmod-SE-doesn-t-match-proc-ttest-SE/m-p/734237#M228761 I guess the distribution is different . T distribution V.S. Normal distribution. Thu, 15 Apr 2021 12:40:13 GMT https://communities.sas.com/t5/SAS-Programming/proc-genmod-SE-doesn-t-match-proc-ttest-SE/m-p/734237#M228761 Ksharp 2021-04-15T12:40:13Z Re: proc genmod SE doesn't match proc ttest SE https://communities.sas.com/t5/SAS-Programming/proc-genmod-SE-doesn-t-match-proc-ttest-SE/m-p/734246#M228762 <P>GENMOD uses maximum likelihood to estimate the scale parameter. TTEST uses a pooled estimate of variance. These are not the same.</P> Thu, 15 Apr 2021 12:46:42 GMT https://communities.sas.com/t5/SAS-Programming/proc-genmod-SE-doesn-t-match-proc-ttest-SE/m-p/734246#M228762 PaigeMiller 2021-04-15T12:46:42Z Re: proc genmod SE doesn't match proc ttest SE https://communities.sas.com/t5/SAS-Programming/proc-genmod-SE-doesn-t-match-proc-ttest-SE/m-p/734828#M228909 <P>Thanks for the quick reply.&nbsp; This is helpful as "<SPAN>The PROC GENMOD scale parameter, in the case of the normal distribution, is the standard deviation."</SPAN></P> Fri, 16 Apr 2021 22:15:41 GMT https://communities.sas.com/t5/SAS-Programming/proc-genmod-SE-doesn-t-match-proc-ttest-SE/m-p/734828#M228909 best_means 2021-04-16T22:15:41Z