Entry
Entries A-Z
Confidence Intervals
A range of numbers that is inferred from a random sample that has a known probability of including the population parameter. One's level of confidence is in the long-term process, not in a particular interval. For example, 95% confidence intervals include the true population parameter (e.g., a population mean, population percentage, or population correlation coefficient) 95% of the time, in the long run; and 99% confidence intervals include the true population parameter 99% of the time, in the long run. Confidence intervals can be made more precise (i.e., made narrower) by using larger sample sizes (e.g., 500 rather than 300) or by relying on a lower level of confidence (e.g., 90% rather than 95% confidence interval). Confidence intervals are contrasted with point estimates, in which ...