Descriptive Statistics: Centre & Spread

Summarising a batch of numbers

• Mean is pulled by outliers; median is resistant.
• Use mean±SD for roughly symmetric data; median±IQR for skewed.
• Five-number summary: min, Q₁, median, Q₃, max → boxplot.

Worked example

Data: 2, 3, 3, 5, 100. Mean = 22.6 (skewed by 100). Median = 3. Prefer median to describe a "typical" value here.