How does sample size affect hypothesis testing?
Introduction to concept
It is quite a while since I did any statistics but I think I can answer this one! The bigger the sample size the more likely it is that it represents the true condition of the population. Thus the more reliable is the test.
The thing is that the bigger the sample size the more work and potential cost is involved. The trick is to obtain just the right size to give a 'significant' indication against which the hypothesis may be assessed.
There is a whole area of statistics that is devoted to reliability of result in relationship to approach to sampling method and size. This is particularly so within the context of mass production and the item produced.