Statistics Refresher II: Choice of Sample Size
One of the important considerations in the planning of any experiment involving statistical analysis of data is the sample size to be used. The appropriate sample size for a given experiment depends upon the hypotheses being tested, the kind of statistical test being applied, the degree of accuracy required by the researcher, and other factors. Generally, it is not appropriate to make an intuitive guess at what the appropriate sample size should be; nor is it always true that "the larger the sample size, the better."
Khamis, H. J.
(1988). Statistics Refresher II: Choice of Sample Size. Journal of Diagnostic Medical Sonography, 4 (4), 176-183.