# Proportion Test Power Calculator

## Information

Calculates the test power for specific sample size and effect size, and draw a power analysis chart.
If you need to calculate the sample size better use the following calculator: proportion sample size.

### Effect

When you choose the effect the tool determines the effect size.
Ignore this field if you know the required effect size.
If you do not know what to do, use the Medium effect.
We recommend to calculate only the priori test power, but you may use this calculator to calculate the post-hoc test power based on the observed effect size.

You may also calculate the required effect size using the "Calculate h".
Example
The null assumption is that the population proportion is 0.7.
You suspect that the proportion is larger. You want to plan research that will reject the null assumption if the population proportion is 0.75 or larger.
1. Press the "Calculate h" button to open the calculation window.
2. Enter P1 = 0.7 and P2 = 0.75.
3. The calculator will update "h effect size" field with h effect size (0.11208).

### Relevant statistical tests

Use this calculator to choose the sample size of one of the following tests:
One Sample proportion Test
Two Sample proportion Test

### Example:

Left-tailed two-sample proportion test, α = 0.05, n1 = 10, n2 = 21.
The test needs to identify a medium effect size: h = 0.5.
Since the h1 is p1 < p2 the effect size should be h=-0.5 otherwise (p1 - p2 < 0) .
The test power is 0.3656151.