- On 18 Nov 2005 at 15:21:33, ShalakaK.-a-.wockhardtin.com sent the message

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Hi

Kindly guide me about T/R Ratio.

When we anaysis data for pilot study, we need to estimate sample size

based on this pilot analysis. I use SAS program to estimmate sample

size. When I use this prog I need to specify alpha, beta, intra

subject cv, T/R ratio and confidence interval.

For estimating sample size I take T/R ratio as 0.90,.95 or 1.00.

Can somebody thro some light, which T/R ratio to be used while

estimating sample size, the one which we get from analysis or those

which I have specified above?

It will be greatful if somebody gives the reference for this.

Regards,

Shalaka Kale

Statistician - On 18 Nov 2005 at 11:07:15, Navdeep Coelho (Navdeep.Coelho.-at-.biovail.com) sent the message

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Hi Shalaka,

For sample size estimation of pivotal studies, one would normally use

the CV% from the pilot results but better to use the T/R ratio of

0.95. Though, you should take into consideration your actual ratio

and see how this affects your sample size estimates. By using 0.95 as

the ratio, you will be assuming that the two formulations will be

within 5% of each other. If the ratio from your pilot results is

quite different from one then this suggests a problem with the

formulation. Also, note that as you deviate from ratio of 1 (higher

or lower), the sample size will increase dramatically.

Hope this helps!

Nav

--

Nav Coelho, M.Sc.

Biostatistician, Pharmacokinetics and Statistics

Biovail Contract Research

Tel: (416) 752-3636 Ext. 369

Email: navdeep.coelho.aaa.biovail.com

URL: www.biovail-cro.com - On 19 Nov 2005 at 12:35:10, =?ISO-8859-1?Q?Helmut_Sch=FCtz?= (helmut.schuetz.at.bebac.at) sent the message

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The following message was posted to: PharmPK

Hi Shalaka!

>For estimating sample size I take T/R ratio as 0.90,.95 or 1.00.

>Can somebody thro some light, which T/R ratio to be used while

>estimating sample size, the one which we get from analysis or those

>which I have specified above?

>

It depends ;-)

Even from a reasonable sized pilot study, estimates of CV are less

reliable than the T/R ratio.

If your main study will use the same batches, I will suggest using the

ratio from the pilot study.

But: since the CV of such importance, I would use not the calculated

value itself, but some upper confidence limit.

If your main study will not use the same batches, it's up to you.

Since batches of both test and reference may be released with an actual

content of +/- 5% of nominal, you may choose whatever you like, but 0.90

is a conservative - but not unreasonable - assumption based on differing

content. In my experience most people go for 0.95.

Some guidelines (Canada, WHO) suggest using a ratio of 1 in sample size

estimation and allow for a correction of the point estimate for the

measured content.

Good luck!

Helmut

--

Helmut Schuetz

BEBAC

Consultancy Services for Bioequivalence and Bioavailability Studies

Neubaugasse 36/11

1070 Vienna/Austria

tel/fax +43 1 2311746

http://BEBAC.at

Bioequivalence/Bioavailability Forum at http://forum.bebac.at

http://www.goldmark.org/netrants/no-word/attach.html - On 21 Nov 2005 at 09:30:52, "Mitesh Gandhi" (mitesh.gandhi.-at-.ranbaxy.com) sent the message

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The following message was posted to: PharmPK

One which you have got from analysis of pilot data.

Mitesh Gandhi

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