What does confidence level equal?

The confidence level reflects the degree of certainty that a statistical estimate lies within a specified range. It quantifies how confident researchers can be about their results when making inferences about a population based on a sample. Mathematically, the confidence level is equal to one minus the significance level, which represents the probability of rejecting the null hypothesis when it is actually true.

In hypothesis testing, the significance level is often set at 0.05, which indicates a 5% risk of concluding that a difference exists when there is none. Therefore, the confidence level would be calculated as 1 - 0.05 = 0.95, meaning there is a 95% confidence that the true parameter lies within the specified confidence interval.

This relationship helps in understanding the balance between making Type I errors (rejecting a true null hypothesis) and maintaining high confidence in our statistical decisions. Hence, knowing that the confidence level equals 1 minus the significance level highlights its fundamental role in statistical inference.