
Preface
One of the most common questions statisticians encounter during interaction
with clinical investigators is “How many subjects do I need for this study?”
Clinicians are often surprised to find out that the required sample size depends
on a number of factors. Obtaining such information for sample size calcula-
tion is not trivial, and often involves preliminary studies, literature review,
and, more than occasionally, educated guess. The validity of clinical research
is judged not by the results but by how it is designed and conducted. Ac-
curate sample size calculation ensures that a study has adequate power to
detect clinically meaningful effects ...