and Sample Size .comFree, Online, Easy-to-Use Power and Sample Size Calculators
no java applets, plugins, registration, or downloads ... just free
Statistical power is a fundamental consideration when designing research experiments. It goes hand-in-hand with sample size. The formulas that our calculators use come from clinical trials, epidemiology, pharmacology, earth sciences, psychology, survey sampling ... basically every scientific discipline.
We take the time to compare our calculators' output to published results. Moreover, our computation code is open-source, mathematical formulas are given for each calculator, and we even provide R code for the adventurous. The validation examples are cited at the bottom of each calculator's page.
We are a group of analysts and researchers who design experiments, studies, and surveys on a regular basis. This site grew out of our own needs. We have benefited from the wealth of knowledge and tools available online. This is our own small way of giving back to the analytics community.