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A confidence interval is an interval estimate of an unknown population parameter. It is constructed according to a random sample from the population and is always associated with a certain confidence level that is a probability, usually presented as a percentage. Commonly used confidence levels include 90%, 95%, and 99%. For instance, a confidence level of 95% indicates that 95% of the time the confidence intervals will contain the population parameter. A higher confidence level usually forces a confidence interval to be wider.

Confidence intervals have a long history. Using confidence intervals in statistical inference can be tracked back to the 1930s, and they are being used increasingly in research, especially in recent medical research articles. Researchersand research organizations such as the American Psychological Association suggest ...

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