https://communities.sas.com/t5/Statistical-Procedures/non-inferioirty-test-for-variances-of-two-groups/m-p/229741#M12103 <P>Does anyone know the SAS code for non-inferiority test for VARIANCES of two group? &nbsp;I see lots on means and proportions but can't find help on variances. &nbsp;Thx!</P> Tue, 13 Oct 2015 16:24:16 GMT msecic 2015-10-13T16:24:16Z https://communities.sas.com/t5/Statistical-Procedures/non-inferioirty-test-for-variances-of-two-groups/m-p/229741#M12103 <P>Does anyone know the SAS code for non-inferiority test for VARIANCES of two group? &nbsp;I see lots on means and proportions but can't find help on variances. &nbsp;Thx!</P> Tue, 13 Oct 2015 16:24:16 GMT https://communities.sas.com/t5/Statistical-Procedures/non-inferioirty-test-for-variances-of-two-groups/m-p/229741#M12103 msecic 2015-10-13T16:24:16Z https://communities.sas.com/t5/Statistical-Procedures/non-inferioirty-test-for-variances-of-two-groups/m-p/229870#M12112 <P>Not something done very often, so it isn't surprising that there is little available. &nbsp;In order to help, do you know what the measure of non-inferiority is for the variances, and how you might be thinking of attacking the problem? &nbsp;Is there literature available that can be worked from?</P><P>&nbsp;</P><P>Steve Denham</P> Wed, 14 Oct 2015 12:28:32 GMT https://communities.sas.com/t5/Statistical-Procedures/non-inferioirty-test-for-variances-of-two-groups/m-p/229870#M12112 SteveDenham 2015-10-14T12:28:32Z https://communities.sas.com/t5/Statistical-Procedures/non-inferioirty-test-for-variances-of-two-groups/m-p/229876#M12116 <P>We can attack it as a difference between the two variances (using d=3), or as a ratio of the two variances (using d=0.5). &nbsp;I think I'll just build a confidence interval around the ratio and if d is outside then conclude non-inferior. &nbsp;Do you think that is sufficient?</P> Wed, 14 Oct 2015 12:44:01 GMT https://communities.sas.com/t5/Statistical-Procedures/non-inferioirty-test-for-variances-of-two-groups/m-p/229876#M12116 msecic 2015-10-14T12:44:01Z https://communities.sas.com/t5/Statistical-Procedures/non-inferioirty-test-for-variances-of-two-groups/m-p/229879#M12117 <P>I would definitely go with the ratio, as it has a known distribution (F distribution) and there are good methods for calculating confidence bounds. &nbsp;If d is outside the bound, then you are probably good to go--just be aware that the lower bound on the F distribution is a bit harder to calculate, and due to the skewness of the distribution, you may need (well, you WILL need) a much larger N to show non-inferiority for the variance, as compared to the mean.</P><P>&nbsp;</P><P>Thinking on this just a bit more--that ratio may be a non-central F, with non-central chi square values needed for the confidence bound. &nbsp;It's been almost 40 years since math stat class, so I would need to dig through some old class notes to be sure.</P><P>&nbsp;</P><P>Steve Denham</P> Wed, 14 Oct 2015 12:53:56 GMT https://communities.sas.com/t5/Statistical-Procedures/non-inferioirty-test-for-variances-of-two-groups/m-p/229879#M12117 SteveDenham 2015-10-14T12:53:56Z https://communities.sas.com/t5/Statistical-Procedures/non-inferioirty-test-for-variances-of-two-groups/m-p/229919#M12120 <P>Thanks so much for the helpful info Steve!</P> Wed, 14 Oct 2015 15:30:00 GMT https://communities.sas.com/t5/Statistical-Procedures/non-inferioirty-test-for-variances-of-two-groups/m-p/229919#M12120 msecic 2015-10-14T15:30:00Z