Sample Size & Statistical Power

These tools are for planning, used before data collection, not for analyzing data you already have. There is no generic sample size that fits every study: every engine here requires a specific design, a target precision or effect, an alpha level, and a target power or confidence level, because those choices are what actually determine how many observations you need.

Every planner shows a sensitivity view and rounds its recommended sample size up to a whole number, but the plausibility of your assumed effect size, event rate, or standard deviation, and whether your actual recruitment can reach the recommended sample, are left for you to judge.