Determine necessary sample size

Hey,

imagine I am comparing two populations. I tested a certain amount of individuals from each population for a specific property, for example speed. I observe a difference between these two groups but it is not sufficiently significant. If this difference really exists, is there a way to do an educated guess how much more individuals I need to test to reach significance?

If so, what would be the Matlab code?

Thanks! Tristan

[Image Analyst]

What confidence do you want? 90%, 95%? http://explorable.com/statistical-significance-sample-size.html