What is a confidence interval (CI)?

A confidence interval (CI) is indeed a range where the true population value likely lies. It reflects the degree of uncertainty around a sample estimate by providing an interval of values that, with a certain level of confidence (commonly 95% or 99%), is believed to encompass the true parameter of interest in the population. The width of the interval indicates the precision of the estimate—the narrower the interval, the more precise the estimate.

For instance, if a CI for a population mean is computed as (45, 55), it suggests that there is a high level of confidence that the actual mean of the population falls within that range. This approach accounts for sampling variability and allows researchers to make inferences about the population based on sample data.

The other answer choices do not accurately capture the concept of a confidence interval. A single score would suggest an exact figure rather than a range of values, the maximum error relates to the precision of the estimate but doesn’t define a confidence interval itself, and the average of observed values does not reflect the uncertainty inherent in sampling nor does it offer a range about the population parameter. Thus, the definition of a CI as a range where the true population value likely lies is a fundamental aspect of statistical inference in research