Plan your sample before you collect a single row. Pick your design and how big an effect you expect — we solve for the sample size using the same statistics engine behind thericerca’s reports. Instant, rule-based, and never guessed.
This planner uses Cohen’s small/medium/large conventions so you don’t need to know your effect size in advance. It reports the sample needed to detect an effect of that size — the real study still checks each test’s assumptions against your data, computes the result in Python, and reports effect sizes, confidence intervals and achieved power.