An introduction to confidence intervals for the population mean mu. These methods are appropriate when we are sampling from a normally distributed population, where the population standard deviation sigma is known. When the population standard deviation is not known, as is usually the case, we need to use a slightly different method (a method based on the t distribution).

Data reference The 2D:4D ratio data is simulated data with the same summary statistics as found in:

Stevenson et al. (2007). Attention Deficit/Hyperactivity Disorder (ADHD) Symptoms and Digit Ratios in a College Sample. American Journal of Human Biology. 19:41–50.