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.
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
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