Critical values are essentially cut-off values that define regions where the test statistic is unlikely to lie.

It is used in test statistic to determine whether to reject the null hypothesis.

**Formula to calculate critical value.**

**Example:**

Suppose the margin of error of a number of experiments is 0.05, if the the standard deviation of the experiments results is 7, calculate the critical value.

Therefore, the critical value is 0.0071.