Sample Size Calculators

for designing clinical research

Need help? Request a consultation from sample-size.net developer Michael Kohn about sample size calculation, study design, data management, or statistical analysis.

About Us

Developers of this Site

Michael A. Kohn, MD, MPP is a retired professor of epidemiology and biostatistics at University of California San Francisco. He was an emergency physician at San Francisco General Hospital until the academic year of 1999-2000 when he did a midcareer fellowship in the ATCR Certificate Program. He has been teaching in UCSF’s Training in Clinical Research Program ever since and, although retired, currently directs courses on clinical epidemiology (Epi 204) and data collection and management (Epi 218). He also co-leads a seminar for second-year masters students. Dr. Kohn is co-author with Dr. Thomas B. Newman of Evidence-Based Diagnosis and director of the Evidence-Based Diagnosis Workshop. He is also a contributing author to Designing Clinical Research. Dr. Kohn provides consultations on clinical research design, sample size calculations, data management, and statistical analysis. Use this form to request a consultation.

Josh Senyak is a software developer, teacher and science writer. His company Quicksilver Consulting develops database applications and websites for scientific researchers and nonprofits. He is co-director for Epi 218, a course on data collection and management through UCSF’s Training in Clinical Research program.

History of Clinical Research Training at UCSF

At UCSF, we began clinical research training three decades ago with the Summer Course in Designing Clinical Research (the “Hulley Course”, directed by Dr. Stephen Hulley). Out of the course arose the textbook by the same name, Designing Clinical Research, the most widely used textbook in clinical research methods, now in its 4th edition. This website’s approach to sample size calculation is based on Chapters 5 and 6, but the material and calculators provided here go well beyond the book.

UCSF’s summer program in clinical research has expanded over the years with the addition of companion courses to Designing Clinical Research. The program has also undergone various name changes and is currently known as the Summer Clinical Research Workshop. In 1992 we began offering the Advanced Training in Clinical Research (ATCR) Certificate Program, a year-long sequel to the Summer Program for scholars interested in additional instruction in the methods of clinical research. In 1999, our programs were greatly expanded as a result of being awarded an NIH K-30 Clinical Research Curriculum Award and we adopted the Training in Clinical Research (TICR) Program as our new name. In particular, this expansion included a more rigorous curriculum in the ATCR Certificate Program and, in 2002, the enrollment of scholars into our two-year Master’s Degree Program in Clinical Research. This specialized degree program in clinical research is the first of its kind in the University of California system.

In 2004, we were awarded an NIH Roadmap K12 grant to begin a Multidisciplinary Clinical Research Scholars Program. This program provides financial support for salary, clinical research training, and conduct of research to a select group of post-doctoral fellows and faculty members for a period of 2 to 5 years.

In 2006, UCSF received a Clinical and Translational Sciences Award from the NIH to create the Clinical and Translational Sciences Institute (CTSI) that now includes the TICR program and the KL2 career development award program.

CTSI Consultation Services

The CTSI’s Consultation Services group provides clinical investigators with advice and assistance in many areas, including study design and implementation, data collection and management, scientific writing, and biostatistics. The need to calculate sample size prompts many investigators to request a CTSI consultation. Often these investigators need much more than just a calculation; they need to understand their study design, identify their primary predictor and outcome, specify how these will be measured, and then start planning their statistical analysis. We developed this website to help meet these needs.