Need to Know

Statistics

The rules you must have ready for the exam.

How to use this: say each rule in your head, then tap Show me to check.

Data types

2 rules

Rule 01

Numerical vs categorical

Numerical: discrete (counts) or continuous (measured). Categorical: ordinal (ordered) or nominal (not).

Rule 02

Primary vs secondary

Primary = you collect it; secondary = from someone else.

1 rule

Rule 03

The three

mean = sum ÷ how many

Median = middle (order first). Mode = most common.

1 rule

Rule 04

Mid-interval mean

Use the middle of each class. Mean = Σ(mid × freq) ÷ Σ(freq).

1 rule

Rule 05

Range & IQR

Range = highest − lowest. IQR = Q₃ − Q₁.

Mathslive.ie · Statistics · Need to Know