Power & Effect Size

Info sheet · Statistics for Psychology & Neuroscience

Author

Andrew Bell

Published

August 13, 2026

Info sheet 0.1 (skeleton) · Prerequisites: what a p-value is; the normal distribution · Give feedback ↗

Working notes for the author — not shown to students once collapsed; remove before publishing.

What you’ll get from this sheet

By the end you should be able to:

  1. Define effect size and statistical power.
  2. Run a power analysis to plan a sample size.

Effect size measures how big an effect is, independent of n; power is the chance of detecting a real effect. Power rises with effect size, α, and — crucially — sample size. Underpowered studies miss real effects and produce flukier significant ones.

[Main idea]

TODO — write the core explanation in transcript voice.

[Interactive demo]

TODO — native <input> + string-built SVG / OJS widget (see any built sheet for the pattern).

See it in code

# TODO
# TODO

TODO — a short question.

TODO — the worked answer.

TODO — a common mistake and how to avoid it.

Where this shows up next

TODO — link to the relevant book chapter.