What is the confidence interval?

• A. The average value of the test metric
• B. The margin of error alone
• C. The range of possible values excluding outliers
• D. The range of possible values accounting for the margin of error, calculated as the test result +/- the margin of error

Answer: (D)

The confidence interval is the range of values that likely contains the true population parameter, reflecting the uncertainty from sampling. It combines a point estimate (the test result) with a margin of error to form an interval. In practice, you take the test result and add and subtract the margin of error to get the interval. The exact width depends on the chosen confidence level, the sample size, and the data’s variability. For example, with a 95% confidence level, if the test result is 100 and the margin of error is 5, the interval is 95 to 105, meaning we’re 95% confident the true value lies in that range. This differs from merely reporting the average, or the margin of error alone, or from excluding outliers; the confidence interval specifically quantifies the range of plausible values for the population parameter around the estimate.