Calculating Power Analysis Online

Calculating power analysis online is crucial for determining the sample size required to detect an effect of a given size with a specified significance level. It helps in planning studies and avoiding underpowered or overpowered experiments.

1. Enter the sample size, effect size, and significance level.
2. Click the ‘Calculate’ button.
3. View the results and chart below.

The power of a test is calculated using the following formula:

Power	= 1 – Φ(-Zα/2 – (Zβ * √(1 – ρ)))

Where:

• Φ is the standard normal cumulative distribution function.
• Z_α/2 is the critical value of the standard normal distribution at the α/2 significance level.
• Z_β is the critical value of the standard normal distribution at the β significance level.
• ρ is the effect size.

Power Analysis for Different Effect Sizes and Sample Sizes

Effect Size	Sample Size	Power

• Always use the most conservative effect size estimate.
• Consider the trade-off between power and sample size.
• Regularly update power calculations as new data becomes available.

What is power in statistics?

Power is the probability that a statistical test will reject the null hypothesis when the alternative hypothesis is true.

For more information, see the UK Office for National Statistics and the Centers for Disease Control and Prevention.