Norvig's article on experiment design is valuable, and a more targeted discussion of sample size with respect to the size of the effect being studied can be fou

Norvig's article on experiment design is valuable, and a more targeted discussion of sample size with respect to the size of the effect being studied can be found at http://en.wikipedia.org/wiki/Statistical_power http://en.wikipedia.org/wiki/Statistical_power, and in some of the references contained within.