
1
Sample Size Determination for Independent
Outcomes
1.1 Introduction
One of the most common questions any statistician gets asked from clinical
investigators is “How many subjects do I need?” Researchers are often sur-
prised 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.
One of the most important aspects in clinical research design is the sample
size estimation.