A 95% confidence interval is commonly used in practice. What percent does it represent?

• A. 90%
• B. 99%
• C. 95%
• D. 85%

Answer: (C)

A confidence interval expresses how often the method would capture the true parameter if we repeated the study many times. A 95% confidence interval means that about 95% of those intervals would contain the true population parameter. In other words, we are 95% confident that this interval includes the true value based on the data and method used. This level is a common balance between precision and reliability—higher levels give wider intervals with more assurance, while lower levels produce narrower intervals with less assurance. So the percent represented by a 95% confidence interval is 95%.