Article Why perform a priori sample size calculation?

Thank you Sir (Prof. Femi) and Dr. Sandip for your references.

Sample size for any study depends on the:

Acceptable level of significance

Power of the study

Expected effect size

Underlying event rate in the population

Standard deviation in the population.

Some more factors that can be considered while calculating the final sample size include the expected drop-out rate, an unequal allocation ratio, and the objective and design of the study.

Go to this website http://raosoft.com/samplesize.html and you will be able to calculate sample size according to your need and take a look at this article which i am attaching below. I think this may help you find the answers you are looking for.

Maybe the following papers will help you

1. Sakpal TV. Sample Size Estimation in Clinical Trial. Perspectives in Clinical Research. 2010;1(2):67-69.

2. Marlies Noordzij Giovanni Tripepi Friedo W Dekker Carmine ZoccaliMichael W Tanck Kitty J Jager.Sample size calculations: basic principles and common pitfalls. Nephrology Dialysis Transplantation, Volume 25, Issue 5, 1 May 2010, Pages 1388–1393.

3. Röhrig B, du Prel J-B, Wachtlin D, Kwiecien R, Blettner M. Sample Size Calculation in Clinical Trials: Part 13 of a Series on Evaluation of Scientific Publications. Deutsches Ärzteblatt International. 2010;107(31-32):552-556. doi:10.3238/arztebl.2010.0552.

4. Bernd Röhrig, Jean-Baptist du Prel, Daniel Wachtlin, Robert Kwiecien, Maria Blettner .Sample Size Calculation in Clinical Trials . Deutsches Ärzteblatt International | Dtsch Arztebl Int 2010; 107(31–32): 552–6

5. Shein‐Chung Chow.Sample size calculations for clinical trials. 08 March 2011.https://doi.org/10.1002/wics.155.

6. Paivand Jalalian .Sample Size Determination for Clinical Trials , 17, 2014.

7. upta K K, Attri J P, Singh A, Kaur H, Kaur G. Basic concepts for sample size calculation: Critical step for any clinical trials!. Saudi J Anaesth [serial online] 2016 [cited 2018 May 3];10:328-31.

Dear Saroj

The sample size depends on the type of your population, is it finite population or infinite population.

In the case of finite population, you can use Slovin formula:

n= N / ( 1+ N * e^2 )

But in the case of an infinite population:

The sample size for any study depends on the standard deviation of the variable ( from previous studies ) and the margin of error you decided. The formula:

n= ( Z^2 * S^2) / E^2

where : Z ( 1.96 for 0.05 and 2.58 for 0.01 )

S = standard deviation from previous studies or pilot study

E = significant level

Also, you can use software to calculate sample size ( SPSS , Minitab , G*power )

My advice to use G*Power . G*Power software is effective tool to calculate sample size for many ranges of experiments. Also, you can determine effect size and power of the test, G*Power is free to download and easy to use after reading the manual, the download link:

http://download.cnet.com/G-Power/3000-2054_4-10647044.html

The link to download G*Power manual:

http://www.gpower.hhu.de/fileadmin/redaktion/Fakultaeten/Mathematisch-Naturwissenschaftliche_Fakultaet/Psychologie/AAP/gpower/GPowerManual.pdf

I hope that be useful for you.

Good Luck

Hi Saroj,

Essentially, there are two main ways of getting a sample size for any study.

1. Based on prior similar or closely related studies

2. Based on known, specific and relevant parameters in the population under study.

For the former you need to review your literature, for the latter, a combination of literature review and online tools such as epi calculators may be helpful.