Final answer:
In statistics, a confidence interval is used to estimate a population mean. A 99.9% confidence interval means that approximately 99.9% of the confidence intervals calculated from repeated samples would contain the true value of the population mean.
Step-by-step explanation:
In statistics, when we use a sample to estimate a population mean, we can calculate a confidence interval to indicate the range of values that likely contains the true population mean. The confidence level measures the level of certainty that the interval contains the true population mean. For example, a 99.9% confidence interval means that if we took repeated samples, approximately 99.9% of the confidence intervals calculated from those samples would contain the true value of the population mean.