# Naked Science Forum

## Life Sciences => Plant Sciences, Zoology & Evolution => Topic started by: itadiki on 08/02/2018 22:42:05

Title: How many research subjects do you need for a study to be statistically valid?
Post by: itadiki on 08/02/2018 22:42:05
Hello,
When publishing research paper how do scientist know how many subject they will need for their study to be valid ?
I am intersting in dog behaviour and training subject for example.
Claudia Fugazza publish a paper.
She used 12 subject for her study.(and 12 other for comparaison How did she know that around this number it would be enough subject to be valid ?

Thanks
Title: Re: How many research subjects do you need for a study to be statistically valid?
Post by: petelamana on 10/02/2018 18:30:12
To have confidence that your study results are representative of the larger population, it is important that you have a large number of randomly-selected subjects in each study group, relative to the estimated population size. The larger the sample size, the less the margin of error.  The following link, www.surveysystem.com/sscalc.htm will provide you with a Sample Size Calculator, but a reasonably good approximation is the simple expression 1/n².

For example:  Say you want a confidence level of 95%, and you want the margin of error to be 6.5%, or 0.065, then...

sample size = 1/n², where n = margin of error.
= 1/(0.065)²
=  236 participants

What was the confidence level of the study Ms. Fugazza performed?  Most researchers use a confidence level of no less than 95%.  At 95%, and only citing 12 subjects, her margin of error would be an enormous 29 (28.29 to be exact).