7. Frequentist I: Confidence Intervals

In previous sessions we considered the concept of estimating population parameters using information from a sample from the population. When we present an estimate of a population quantity, it is important to also provide a measure of how precise that estimate is. Do we believe it is close to the true value? Can we provide a range of values within which we believe the true value lies?

This is the purpose of a confidence interval, often abbreviated by CI. Loosely speaking, a confidence interval provides a range of values for the population parameter which our observed data are consistent with.

Intended learning outcomes

By the end of this session you will be able to:

  • correctly interpret a 95% confidence interval interval

  • describe properties of a 95% confidence interval over repeated sampling

  • calculate a 95% confidence interval for the mean

  • use resampling (bootstrapping) approaches to obtain percentile confidence intervals