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El-Aura
Calcite | Level 5

Hi there! 

 

I'm trying to replicate a two-sample survival design using proc seqdesign. It has 2 stages (one interim at 73% of the information, one final at 100% information). One-sided alpha=0.025 power=0.835 (beta=0.165). O'Brien Fleming boundary will be implemented for efficacy and the Haybittle-Peto boundary will be implemented for futility. Assumed hazard ratio=0.58. Median survival time in the control arm is 42 months. Here're my codes:

ods graphics on;
proc seqdesign stopprob errspend boundaryscale=pvalue;
OneSidedOBFandHP: design alt=lower alpha=0.025 beta=0.165 nstages=2
method(reject)=obf method(accept)=hp(Z=0.489)
stop=both(betaboundary=nonbinding) info=cum(0.73 1);
model=twosamplesurvival (hazardratio=0.58 nullmedsurvtime=42);
ods output Boundary=Bnd_Time;
run;
ods graphics off;

But the results (stopping p-value boundaries) are not the same as the design I'm trying to replicate which has boundaries like:

 

El-Aura_0-1619470168871.png

 

A friend said that the problem is with "alt=lower" since for futility, alt should be "upper". But you can't specify two alts in seqdesign right? So is this the problem? How should I modify my codes to get the design I want to replicate (the screenshot above)? 

 

Many thanks!!!

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