Hey everyone! I am a medical student and I was wondering how to calculate sample size for a research! I usually rely on statisticians but it would be nice to learn this kind of stuff. I found some online calculators that calculate the sample size on the basis of population, confidence level and confidence interval. I know the population and confidence level, but I have no idea how to decide/obtain the confidence interval. Can anyone suggest an online calculator/software/formula that might help me with this stuff?
Dear Hassan,
You may find this software helpful, www.mc.vanderbilt.edu/prevmed/ps/.
Martin Bland's page on sample size calculation is also very good
http://www-users.york.ac.uk/~mb55/msc/trials/sampsz.htm#howlarge
Similarly this page has some excellent advice and references.
http://www-users.york.ac.uk/~mb55/guide/size.htm
Best wishes
Joe
Dear Hassan,
Some softwares, using the famous open source R, permit calculation of sample size online.
For example, the French speaking site http://marne.u707.jussieu.fr/biostatgv/?module=etudes/sujets# is one possibility. It think it could help you, at least partially.
Patrice
Dear Hassan,
There area lot of issues to consider when calculating the sample size for a study. There are some good free resources such as EpiInfo 7 (http://wwwn.cdc.gov/epiinfo/html/downloads.htm) and OpenEpi (http://www.openepi.com/OE2.3/Menu/OpenEpiMenu.htm).
Good luck
Andre
Dear Hassan
these are 2 good programs:
1-WHO standard sample size calculation software
2-G-power
You can download (they are both free) and use either of them.
Dear Hassan,
You may find this software helpful, www.mc.vanderbilt.edu/prevmed/ps/.
Martin Bland's page on sample size calculation is also very good
http://www-users.york.ac.uk/~mb55/msc/trials/sampsz.htm#howlarge
Similarly this page has some excellent advice and references.
http://www-users.york.ac.uk/~mb55/guide/size.htm
Best wishes
Joe
try Open epi software .Open Source Epidemiologic Statistics for Public Health, Version 2.3. for calculating sample size it's free .... it's user friendly software
Your power analysis should drive your sample sizing.
This paper by Cohen is pretty good.
http://web.vu.lt/fsf/d.noreika/files/2011/10/Cohen-J-1992-A-power-primer-kokio-reikia-imties-dyd%C5%BEio.pdf
JAMA has a new series on statistics, application and interpretation, including this paper that might be of interest:
Stokes L. Sample Size Calculation for a Hypothesis Test. JAMA. 2014;312(2):180-181. doi:10.1001/jama.2014.8295.
Dear Hassan Khan, In order to work out a good sample size, random, sample generator is available at: http://www.psychicscience.org/random.aspx (Allan Bryman and Duncan Cramer, 2009). It will give a food for thought.
You can use the Gpower or NCSS or IBM sample size or online website for your sampling
Dear RG colleague,
Determining the sample sizes involve resource and statistical issues. Usually, researchers regard 100 participants as the minimum sample size when the population is large. However, In most studies the sample size is determined effectively by two factors: (1) the nature of data analysis proposed and (2) estimated response rate.
For example, if you plan to use a linear regression a sample size of 50+ 8K is required, where K is the number of predictors. Some researchers believes it is desirable to have at least 10 respondents for each item being tested in a factor analysis, Further, up to 300 responses is not unusual for Likert scale development according to other researchers.
Another method of calculating the required sample size is using the Power and Sample size program (www.power-analysis.com).
Regards,
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