Confidence intervals are commonly expressed at which percentile levels?

Confidence intervals are commonly expressed at which percentile levels?

• A. 90th percentile
• B. 95th percentile
• C. 90th or 95th percentile
• D. 99th percentile

Answer: (C)

Confidence intervals carry a level of certainty about where the true parameter lies. The most common levels used in practice are 90% and 95%; 95% is the standard choice because it offers a good balance between precision and reliability, while 90% gives a narrower interval when you’re willing to accept a bit more risk of missing the true value. In some contexts, 99% is used when higher confidence is required, but it’s less common as a default because it produces a wider interval. So, mentioning either 90% or 95% captures the typical options you’ll see most often, which is why that choice fits best.

Confidence intervals carry a level of certainty about where the true parameter lies. The most common levels used in practice are 90% and 95%; 95% is the standard choice because it offers a good balance between precision and reliability, while 90% gives a narrower interval when you’re willing to accept a bit more risk of missing the true value. In some contexts, 99% is used when higher confidence is required, but it’s less common as a default because it produces a wider interval. So, mentioning either 90% or 95% captures the typical options you’ll see most often, which is why that choice fits best.