topic Graph builder - confidence intervals for categorical variable in Discussions https://community.jmp.com/t5/Discussions/Graph-builder-confidence-intervals-for-categorical-variable/m-p/672107#M85994 <P>When applying the Line Of Fit option in graph builder with a categorical variable on the x-axis you can calculate confidence intervals for each of the group means. If you choose <EM>unequal variance</EM> the confidence intervals are based on the individual group variances but how is the degrees of freedom for the t-distribution calculated? It appears to be based not on the individual sample sizes but the overall sample size. I wonder what is the theoretical rationale behind the calculation.&nbsp;&nbsp;</P> Tue, 29 Aug 2023 09:46:18 GMT StefanC 2023-08-29T09:46:18Z Graph builder - confidence intervals for categorical variable https://community.jmp.com/t5/Discussions/Graph-builder-confidence-intervals-for-categorical-variable/m-p/672107#M85994 <P>When applying the Line Of Fit option in graph builder with a categorical variable on the x-axis you can calculate confidence intervals for each of the group means. If you choose <EM>unequal variance</EM> the confidence intervals are based on the individual group variances but how is the degrees of freedom for the t-distribution calculated? It appears to be based not on the individual sample sizes but the overall sample size. I wonder what is the theoretical rationale behind the calculation.&nbsp;&nbsp;</P> Tue, 29 Aug 2023 09:46:18 GMT https://community.jmp.com/t5/Discussions/Graph-builder-confidence-intervals-for-categorical-variable/m-p/672107#M85994 StefanC 2023-08-29T09:46:18Z Re: Graph builder - confidence intervals for categorical variable https://community.jmp.com/t5/Discussions/Graph-builder-confidence-intervals-for-categorical-variable/m-p/684134#M86982 <P>I will answer my own question:) It turns out that the confidence intervals given by JMP are too narrow. "Correct" confidence intervals can be calculated for example in SAS with the proc mixed procedure allowing a heterogeneous variance structure and specifying the degrees of freedom method as ddfm=KenwardRoger.&nbsp;</P> Thu, 05 Oct 2023 11:30:31 GMT https://community.jmp.com/t5/Discussions/Graph-builder-confidence-intervals-for-categorical-variable/m-p/684134#M86982 StefanC 2023-10-05T11:30:31Z