Fundamentals, context and study design

Variation is at the heart of statistics. It’s everywhere, and without it, data are not very interesting. Understanding this is central to the tasks we carry out in visualising, summarising and analysing data.

What makes the variable random is that — unlike the kind of variable we see in a quadratic equation, for example — we cannot say what the observed value of the random variable is until we actually carry out the procedure.

“You can’t fix by analysis what you bungled by design.” Light, Singer and Willett (1990, page v). Good study design is paramount. Here are the three Rs of study design.

A basic lesson in data recording and management is to carefully and accurately describe the variables in a data file. This includes describing the measurement scale used and the units for numerical variables.