S1 · Statistics · STAT.SPREAD.INTRO

Spread and quartiles basics

Intuition

Understand first, compress later.

Statistics describes data and separates visible patterns from random variation.

Switch representations

Box plotn = 13 · quartiles by linear interpolation

middle 50 % (IQR)medianoutlier

Five-number summary: min 15, Q₁ 25, median 30, Q₃ 40, max 50. The box holds the middle 50 % of the data and the interquartile range is 15. The whiskers reach the most extreme value within 1.5·IQR; one value lies beyond that fence and is drawn individually as an outlier.

Formal view

You can spread and quartiles basics when you can recognise the underlying objects, select valid rules and check each step for equivalence or logical implication.

Why does it work?

This skill sits on a prerequisite network. If a step is unstable, repair the missing prerequisite instead of merely doing more items of the same type.