Confidence intervals

Estimation vocabulary: what an interval captures, how wide it is, and what confidence means.

5 terms

Confidence intervalA confidence interval is a range of plausible values for a population parameter, built from a sample as the estimate plus or minus a margin of error.Confidence levelThe confidence level is the long-run percentage of confidence intervals, built the same way from repeated samples, that would capture the true parameter.Critical valueA critical value is a cutoff from a reference distribution, such as z or t, that sets a confidence interval's width or a test's rejection boundary.Degrees of freedomDegrees of freedom are the number of values free to vary when computing a statistic, and they set the exact shape of a t or chi-square distribution.Margin of errorThe margin of error is how far a point estimate may reasonably sit from the true parameter; it equals the critical value times the standard error.