Define CI.

Define CI.

• A. A range of values that includes the real mean for the population
• B. A measure of variability within the sample
• C. A test of statistical significance
• D. The sample size of the study

Answer: (A)

A confidence interval is a range of values calculated from sample data that is used to estimate a population parameter, typically the mean, and to express how precise that estimate is. The interval is constructed so that, if we repeated the study many times, a chosen proportion (like 95%) of the intervals would contain the true population mean. So describing it as a range that plausibly includes the population mean captures its purpose: providing an estimate plus the uncertainty around it. The other options describe different concepts: a measure of variability within the sample refers to spread such as standard deviation or standard error, not the interval itself; a test of statistical significance relates to whether observed results could arise by chance (p-values, hypotheses); and the sample size is simply how many observations were collected, not an interval.

A confidence interval is a range of values calculated from sample data that is used to estimate a population parameter, typically the mean, and to express how precise that estimate is. The interval is constructed so that, if we repeated the study many times, a chosen proportion (like 95%) of the intervals would contain the true population mean. So describing it as a range that plausibly includes the population mean captures its purpose: providing an estimate plus the uncertainty around it.

The other options describe different concepts: a measure of variability within the sample refers to spread such as standard deviation or standard error, not the interval itself; a test of statistical significance relates to whether observed results could arise by chance (p-values, hypotheses); and the sample size is simply how many observations were collected, not an interval.