Scatter Diagrams and Correlation
Understand Scatter Diagrams and Correlation for GCSE Statistics with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA and Edexcel. Scatter diagrams show the relationship between two variables, described as positive, negative or no correlation.
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA and Edexcel specifications. Every worksheet comes with a full mark scheme.
Topic overview
A scatter diagram plots bivariate data with one variable on each axis, and the pattern of points reveals whether the variables are related.
Correlation describes that relationship. Positive correlation means that as one variable increases the other tends to increase, and the points slope upwards. Negative correlation means that as one increases the other tends to decrease, and the points slope downwards. No correlation means the points show no pattern.
Strength matters as well as direction. Points lying close to a straight line show strong correlation; points widely scattered around it show weak correlation. Both the strength and the direction should be given when describing correlation, along with an interpretation in context.
Revision notes
Types of correlation
Positive: as one variable increases, the other tends to increase. Points slope upwards.
Negative: as one increases, the other tends to decrease. Points slope downwards. None: the points show no discernible pattern.
Strength of correlation
Points lying close to a straight line indicate strong correlation.
Points widely scattered around the line indicate weak correlation. Describe both strength and direction — 'strong positive correlation' rather than just 'positive'.
Describing in context
State what the correlation means for the variables involved.
Not just 'positive correlation' but 'as the number of hours revised increases, the test score tends to increase'. The word 'tends' matters, because correlation describes a trend rather than a rule.
Key points
- Scatter diagrams show bivariate data.
- Positive correlation slopes upwards.
- Negative correlation slopes downwards.
- No correlation shows no pattern.
- Points close to a line mean strong correlation.
- Describe both strength and direction.
Worked examples
Example 1
A scatter diagram shows points sloping downwards and lying close to a straight line. Describe the correlation. [2 marks]
Working
Example 2
Explain the difference between strong and weak correlation. [2 marks]
Working
Example 3
A scatter diagram of hours revised against test score shows positive correlation. Interpret this in context. [2 marks]
Working
Common mistakes
Giving direction without strength.
Describe both — 'strong positive' rather than just 'positive'.
Describing correlation without context.
Say what it means for the actual variables.
Saying correlation means one causes the other.
Correlation shows a relationship, not causation.
Using 'always' rather than 'tends to'.
Correlation describes a trend, not a rule that holds for every point.
Exam tips
- Give both strength and direction.
- Interpret the correlation in context.
- Use 'tends to' rather than 'always'.
- Never claim causation from correlation alone.
Key terms
- Scatter diagram
- A plot of bivariate data with one variable per axis.
- Correlation
- A relationship between two variables.
- Positive correlation
- Both variables increasing together.
- Strength
- How closely the points follow a straight line.
Related topics
Written and reviewed against the current AQA and Edexcel specifications. Spotted an error? Let us know.