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SciClone Pharmaceuticals, Inc. Message Board

  • heldnova heldnova Dec 11, 2005 5:49 PM Flag

    From the 2004 RBC report

    The phase III design was finalized in consultation with the FDA and is powered to
    demonstrate a 10-percentage point difference between the treatment arm and
    placebo. Management expects to see an SVR rate of less than 5% for placebo,
    suggesting that an SVR rate greater than 15% in the Zadaxin arm will be statistically
    significant. There will be no interim looks at the data and results are expected late in
    2005.

    Rick

    SortNewest  |  Oldest  |  Most Replied Expand all replies
    • 22% and dancin'

    • >>>In the case of Interferon and Peg-Interferon, the INterferon was getting about a 50% success rate. Sizing their trial to prove a 10% difference meant that they wanted to be sure that if their sample showed 55% or greater (10 percent greater than 50%) then that difference is significant statistically. They achieved 56-58%. <<<

      blandis,

      I think in the case you cite , the interpretation of the 10% difference could be just as you describe , and that what we're talking about here is a difference in common language , not in statistics.

      >>> You need much larger samples for the case of 50/60 than you do for 2/12. I don't think you need a sample anywhere near 250 to show 12 is different from 2(so long as you aren't assuming the statistical variance of the data to be very large) <<<

      I don't disagree that a 10% difference is easier to demonstrate as the comparator value gets closer to zero but as you change what you say to 15 vs. 5 or 20 vs. 10 , which may be numbers that SCLN management had to consider as possible , then I think the trial was probably accurately powered. I do think it's way off base to say that this trial could demonstrate with statistical significance the difference between 5 and 5.5% or for that matter 1% and 1.1% (both 10% differences , by your preferred definition ).The reason is that the variances are significant . This is not like fipping a coin and measuring heads and tails. There is variance in the measurement of viral load , there is probably a very considerable variance in the histology readings as they are done by humans , not machines , and there are between-site variances in the data that may be considered in the analysis.

      Just take a look at the patient numbers you get when you multiply those numbers , say 1% vs. 1.1% , by a trial arm size of 250 , and you'll realize that somebody will have to be dissected to provide the extra .25 of a patient that would be expected to get an SVR. At some point common sense tells you what a statistical calculator does not.

    • I tried to call today, but no one was answering. Pense

    • I think you are right in your interpretation.

      If I remember right there were suppose to be 500 people enrolled in each arm of the study. Even assuming we have a large drop out rate in the 500 arm study soon to be published, it shouldn't take a three fold increase in SVR rate (from 5% to 15%) to show statistical significance in that large of a population size.

      May the pvalue be with us!

    • I wonder if anyone is picking up the phone Sunday night at Scln.

    • We can agree to differ but I believe you are wrong.

      I have never seen anyone set up a trial to show the kind of differences you are talking about, particularly with small numbers for success rates. It is pretty easy to show that a trial value of 12 is significaltly different than a population value of 2. It is a little bit harder to show that 20 is different than 10 and much harder to show that 60 is better than 50 (these difficulties assume something about the statistical variance). You need much larger samples for the case of 50/60 than you do for 2/12. I don't think you need a sample anywhere near 250 to show 12 is different from 2(so long as you aren't assuming the statistical variance of the data to be very large)

    • Since we may well have the final #s within the next 12 hours, it would be entertaining to see guesses as to SVR from anyone who would care to hazard a guess. So far I am aware of the following:

      Tc----------------15%
      WCD-------------15%
      sno---------------6-8%
      Mh----------------15-20%
      heldnova----------20%

      Of course, some of these #s were given before the latest round of discussion on the board and their owners may wish to update them. But it's Sunday night, not much else going on, and it would be fun to see who comes closest. Anyone care to place or fine tune their bets? Maybe the winner should be addressed with additional respect or something for the following week. For instance, "How did you guess 8%, sno? (hail, sno)"
      Tc

    • >>>The phase III design was finalized in consultation with the FDA and is powered to
      demonstrate a 10-percentage point difference between the treatment arm and
      placebo. Management expects to see an SVR rate of less than 5% for placebo,
      suggesting that an SVR rate greater than 15% in the Zadaxin arm will be statistically
      significant. There will be no interim looks at the data and results are expected late in
      2005.<<<

      So that means single digits would not be statistically significant, correct? You'd better be wrong about your guess, sno. Tc

 
SCLN
6.79-0.11(-1.59%)Aug 27 4:00 PMEDT

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