# Statistical power calculators

The power calculator computes the test power based on the sample size and draw an accurate power analysis chart.

**Larger sample size increases the statistical power.**

**The test power is the probability to reject the null assumption, H**_{0}, when it is not correct.

**Power = 1- β**.

Researchers usually use the power of **0.8** which means the Beta level (β), the maximum probability of type II error, failure to reject an incorrect H_{0}, is **0.2**.

The commonly used significance level (α), the maximum probability of type I error, is **0.05**.

The Beta level (β) is usually four times as big as the significance level (α), since rejecting a correct null assumption consider to be more severe than failing to reject incorrect null assumption.

### Power analysis chart

The calculators create the following dynamic chart:

**Region of Acceptance** - accept the null hypothesis if the statistic value in this area.

**Region of Rejection** - reject the null hypothesis if the statistic value in this area.

Grey area - The probability to accept the H_{0} when H_{0} is correct.

Significance level (α) - The probability to reject the H_{0} when H_{0} is correct.

β: the probability to accept the H_{0} when H_{1} is correct.

Test power: The probability to reject the H_{0} when H_{1} is correct.