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Significance, Confidence Level, and Confidence Interval

Stephanie Glen disambiguates three commonly confused but quite different terms:

In a nutshell, here are the definitions for all three.

1. Significance level: In a hypothesis test, the significance level, alpha, is the probability of making the wrong decision when the null hypothesis is true.
2. Confidence level: The probability that if a poll/test/survey were repeated over and over again, the results obtained would be the same. A confidence level =  1 – alpha. 
3. Confidence interval: A range of results from a poll, experiment, or survey that would be expected to contain the population parameter of interest. For example, an average response. Confidence intervals are constructed using significance levels / confidence levels.

Read on for several examples and more elaboration.