Statistician how-to

How to Calculate Sample Size for a Study

Too small studies miss real effects.

Updated By the Career Education Institute Curriculum Team
Quick answer

Too small studies miss real effects. In short: define; estimate; choose, then complete the remaining steps below.

Step by step

  1. Define the outcome.

  2. Estimate effect size.

  3. Choose significance level.

  4. Choose power.

  5. Calculate.

  6. Add for dropouts.

Safety reminders for statisticians

  • Protect patient data
  • Follow research ethics
  • Avoid p-hacking
  • Disclose limitations

p-value · Confidence interval · Sample size · Power · Regression · Randomization: see the full statistician glossary.

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