Sample size determination for clinical research.

Calculating the sample size is a most important determinant of statistical power of a study. A study with inadequate power, unless being conducted as a safety and feasibility study, is unethical. However, sample size calculation is not an exact science, and therefore it is important to make realistic and well researched assumptions before choosing an appropriate sample size accounting for dropouts and also including a plan for interim analyses during the study to amend the final sample size.