Dear all, I want identify genetic variants for Autism in proband trio data. The initial plan is using TDT test to do the analysis. However, I do not know if my sample size is enough for that. It would be appreciated if someone can give me a clue.
It depends on many factors.
You can carry out some power calculations to get some ideas on how many families will require to achieve >80% power for your particular study.
http://zzz.bwh.harvard.edu/gpc/
https://gump.qimr.edu.au/general/manuelF/power_tdt/main.html
You can also use this package for R. It can calculate the number of trios directly.
https://cran.r-project.org/web/packages/powerpkg/powerpkg.pdf
Dear Bochao
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 the attached table to estimate the suitable sample size. Or 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
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