Test power and sample size

There are several ways we can approach determining the sample size. One possibility is to estimate how large the sample should be to reflect the population. Another possibility is to estimate the sample size for the situation of applying specific statistical tests. Then, in addition to the necessary sample size, we may be interested in the power of those tests. The first, and seemingly easier approach, is presented in subsection Sample size determination, the second in subsection Power and size for a test.