A-Level Maths: Statistics Revision

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What does a larger standard deviation tell you about a data set?

Statistics is a core part of A-Level Maths. Revise the key concepts and common mistakes below, then lock them in with the free games.

Key concepts

MeanSum ÷ number of values; sensitive to outliers.

MedianMiddle value when ordered; resistant to outliers.

ModeMost frequent value; data may be bimodal or have no mode.

RangeMax minus min — a simple measure of spread.

VarianceAverage squared deviation from the mean.

Standard deviationσ = √variance; same units as data.

Scatter diagramPlot pairs (x,y) to spot patterns in bivariate data.

Correlation rPearson r between -1 and +1: sign and strength of linear relationship.

Interpretationr near 1 strong positive; near -1 strong negative; near 0 weak/none.

Regression liney = a + bx fits 'line of best fit' minimising squared errors.

Slope bExpected change in y per unit change in x.

Correlation vs causationHigh r doesn't prove causation; lurking variables matter.

Normal distributionBell-shaped, symmetric about mean μ, parameter σ².

NotationX ~ N(μ, σ²) means X is normal with mean μ, variance σ².

Learn Statistics step by step

Free interactive mini-lessons: short screens, worked examples and quick checks. Pick your exam board to open its course map, then tap L on this topic:

AQA CCEA Edexcel OCR

Common mistakes to avoid

Questions where students often pick the tempting wrong answer — make sure you know the right one:

What does a larger standard deviation tell you about a data set?✗ The mean of the data set is larger. ✓ The data values are more spread out around the mean.

If a data set has an extreme outlier, which average is most affected?✗ The median is most affected because the outlier shifts the middle. ✓ The mean — because every value (including the outlier) contributes to it.

If two variables are strongly correlated, what can you conclude?✗ Strong correlation means that one variable causes the other. ✓ They vary together — but correlation alone does not establish that one causes the other.

Standard normal has μ and σ✗ 1 and 0 ✓ 0 and 1

About 95% of data lies within✗ 1σ of mean ✓ 2σ of mean

Practise Statistics — free games

Test yourself with these quick revision games for this topic:

▶ Two Truths, One Lie ▶ Reveal Race ▶ Connections Grid ▶ Falling Words ▶ Word Web

See all 22 games in the Revision Arcade →

Statistics

Key concepts

Common mistakes to avoid

Practise Statistics — free games

More A-Level Maths topics