A confidence interval is generally represented as a percentage figure. Let’s see what a confidence level of 95% signifies. When the same experiment is carried out using different populations, the results will fall within the margin of error 95% of the time.

If that does not happen, it means that the population used for the initial calculation was not a representative sample. Commonly used confidence intervals are 90%, 95%, and 99%. For the purposes of calculating confidence intervals, α is used. α is the inverse of the confidence interval.

For a confidence interval of 90%, α=0.10.

For a confidence interval of 95%, α=0.05.

For a confidence interval of 99%, α=0.01.

α is called the significance level.