Some time might be usefully spent in reading "E9 Statistical Principles for Clinical Trials" available from the US FDA website: http://www.fda.gov/cder/guidance/ICH_E9-fnl.PDF
Frank Isackson
-----Original Message-----
>From: Jay Warner <[log in to unmask]>
>Sent: Jan 26, 2006 8:40 AM
>To: [log in to unmask]
>Subject: Re: sample size in non-inferiority trial
>
>For the benefit of us uninformed folks, could someone write a short
>piece giving equivalent words (operational definitions) for
>
>Non-inferiority
>
>equivalence
>
>two-side hypothesis for alpha test (group A is equal to group B/
>Group A is different than Group B)
>
>one-side hypothesis for alpha test (group A is equal or less than
>group B/group A is greater than group B)
>
>one-side and/or two-side beta test (power test) for groups A and B
>comparisons.
>
>If my suspicions are right, then Ioanna's questions can be re-phrased
>into typical/common statistical language, and the issue of alpha
>level (0.05 or 0.025) will become 'obvious.'
>
>Besides, I want to know the terms used by medical people. :)
>
>Jay
>On Jan 26, 2006, at 9:33 AM, ioanna gioni wrote:
>
>> Dear all,
>>
>> I need to calculate the sample size for a non-inferiority trial
>> (normal data).
>> I have an issue with the choice of alpha in the sample size
>> calculation formula. I am not sure if I need to set my type error I
>> (alpha) at half the conventional type I error used in two-sided
>> confidence intervals.
>> Unfortunately, I don?t have access to any sample size calculations
>> book that deals with non-inferiority/equivalence issues.
>> Searching in the Internet I found various examples where some
>> calculate the sample size setting alpha to be 0.05 and some setting
>> alpha to be 0.025.
>> I know that for the analysis I need to either calculate a two-sided
>> 95% confidence interval (equal-tailed) and then use the lower bound
>> for testing the hypothesis or calculate one-sided intervals with a
>> coverage probability of 97.5%. My issue is if in the sample size
>> calculation I set alpha as 0.05 or 0.025.
>>
>> Any help would be appreciated,
>>
>> Ioanna
>>
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>
>Jay Warner
>Principal Scientist
>Warner Consulting, Inc.
>4444 North Green Bay Road
>Racine, WI 53404-1216
>USA
>
>Ph: 262.634.9100
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>
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