Hello,
I am running an analysis for a non-inferiority design with proportions. The current analysis is an interim analysis where I am applying Pocock boundary (significance boundary pvalue = 0.0310).
The analysis is comparing proportion difference. The non-inferiority margin is -0.10.
The code I am using is:
proc freq data=a order=data; tables group*Response / riskdiff(noninf margin=.10 method=fm norisks); weight Count; run;
Usually in a non-inferiority setting I would compare the lower bound of the confidence interval to the non-inferiority margin. If the lower bound is greater than margin this indicates non-inferiority. However, because this is an interim analysis and I have a pvalue boundary, I need to compare the pvalue that is generated to the pvalue significance boundary as well.
The SAS output from the above code shows the Farrington-Manning non-inferiority pvalue and confidence interval. My question is what happens if the pvalue boundary is not crossed - for example if the pvalue comes out to be 0.04 (compared to boundary of 0.03) then I cannot stop the trial for efficacy - i.e non-inferiority not shown. However the lower bound of the confidence interval is greater than the non inferiority margin - which would indicate non-inferiority has been shown.
Is there an option in SAS that would reconcile these? If not, which would be the more correct measure to use - the NI pvalue or the lower bound CI, to determine whether the study can stop at the interim?
Thank you.
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