ABSTRACT
One of the most common questions any statistician gets asked from clinical investigators is “How many subjects do I need?” Researchers are often surprised to find out that the required sample size depends on a number of factors and they have to provide information to a statistician before they can get an answer. Clinical research is judged to be valid not by the results but by how it is designed and conducted. The cliche “do it right or do it over” is particularly apt in clinical research.
