# Confidence Interval

In a confidence interval, it is estimated that a population parameter has a certain probability, generally 90%, 95% or 99%.

The **confidence limits** are the two extreme values of the confidence interval which define the range.

### Confidence Level

The confidence level is the probability that the parameter estimate is within the confidence interval. It is represented by **(1 − α)**, where **α** is the **significance level**.

### Critical Values

A critical value is the value corresponding to a given significance level.

1 − α | α/2 | z_{α/2} |
---|---|---|

0.90 | 0.05 | 1.645 |

0.95 | 0.025 | 1.96 |

0.99 | 0.005 | 2.575 |

#### α/2 = 0.05 1 − α = 0.90

#### α/2 = 0.0251 − α = 0.95

#### α/2 = 0.0051 − α = 0.99

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