sample size for 3 groups?

[Doaa]

Hello, 

I need help in estimate sample size for 3 groups.

I will conduct double blind randomized placebo control clinical trial , i will make 3 arms .

i will estimate the effect of drug x in weight loss

what the minimum sample size I need in each group ??

[Peter Flom]

The sample size you need depends on:

 

1. Desired power – usually 0.8 or 0.9 but you can pick
2. Desired alpha – usually 0.05 or 0.01 but you can pick
3. Effect size that you want to have that power to detect.  Effect size is measured in different ways depending on your statistical test. That will depend on your dependent variable and how It is measured and what effect sizes have been found in the past and so on

 

Peter

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[John Whittington]

At 13:42 11/03/2018, Peter Flom wrote:

The sample size you need depends on:

1. Desired power - usually 0.8 or 0.9 but you can pick

2. Desired alpha – usually 0.05 or 0.01 but you can pick
3. Effect size that you want to have that power to detect.  Effect size is measured in different ways depending on your statistical test. That will depend on your dependent variable and how It is measured and what effect sizes have been found in the past and so on

Indeed, but I would add to that a fourth item (usually the most difficult one) ... namely an estimate of the variability of the dependent variable.

Kind Regards,

John

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[Martin Holt]

Doaa~

GPower software (free) should prove useful in this scenario. Explore the net to find out more.

For example:

LibGuides: Statistical & Qualitative Data Analysis Software: About GPower

LibGuides: Statistical & Qualitative Data Analysis Software: About GPower This guide contains information for current faculty, staff, and students at Kent State about statistical and qua...

 Kind Regards

Martin 

Freelance Medical Statistician

If you can't explain it simply, you don't understand it well enough.....Einstein

Concise

Encyclopedia

of Biostatistics for

Medical Professionals 

Martin P. Holt

https://www.crcpress.com/Concise-Encyclopedia-of-Biostatistics-for-Medical-Professionals/Indrayan-Holt/9781482243871

Linked In: 

https://www.linkedin.com/in/martin-holt-3b800b48?trk=nav_responsive_tab_profile

---

From: Doaa <doaa.ab...@gmail.com>
To: MedStats <meds...@googlegroups.com>
Sent: Sunday, 11 March 2018, 10:32

Subject: {MEDSTATS} sample size for 3 groups?

[Martin Holt]

Doaa~

Following on from my last post....

Plug these four into GPower

Best Wishes

Martin

 

Freelance Medical Statistician

If you can't explain it simply, you don't understand it well enough.....Einstein

Concise

Encyclopedia

of Biostatistics for

Medical Professionals 

Martin P. Holt

https://www.crcpress.com/Concise-Encyclopedia-of-Biostatistics-for-Medical-Professionals/Indrayan-Holt/9781482243871

Linked In: 

https://www.linkedin.com/in/martin-holt-3b800b48?trk=nav_responsive_tab_profile

---

From: John Whittington <Joh...@mediscience.co.uk>
To: meds...@googlegroups.com; meds...@googlegroups.com
Sent: Sunday, 11 March 2018, 16:27
Subject: RE: {MEDSTATS} sample size for 3 groups?

[Doaa Abdulsalam]

Thanks Martin 
I will try it .......

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[Doaa Abdulsalam]

Thanks a lot for all of you