In the introduction, we mention a “confidence level,” but didn’t really elaborate on what we meant. So, let’s establish some vocabulary, both mathematically and in plain English

• Sample: A collection of measurements from a subset of a population. Mathematically, this is a vector $\vec{x}=[x_1,x_2,\dots,x_n]$ made of $n$ elements ($n$ is called the sample size)
• Statistic: Some summary measurement that can be computed