This topic summary covers Knowledge Organiser: Scatter Graphs within Scatter Graphs for GCSE Mathematics. Revise Scatter Graphs in Statistics for GCSE Mathematics with 14 exam-style questions and 20 flashcards. This topic appears less often, but it can still be a useful differentiator on mixed-topic papers. It is section 8 of 8 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
Knowledge Organiser: Scatter Graphs
Key Terms
- Scatter graph: A graph plotting two variables to show whether they are related
- Correlation: A relationship between two variables
- Positive correlation: As one variable increases, the other increases
- Negative correlation: As one variable increases, the other decreases
- Line of best fit: A straight line that best represents the trend of the data
- Outlier: A point that does not fit the general pattern
Must-Know Facts
- Describe correlation as: strong/weak AND positive/negative/none
- The line of best fit must balance points equally above and below
- Outliers are ignored when drawing the line of best fit
- Correlation does NOT prove causation
- Interpolation (reading within the data range) is more reliable than extrapolation
- Always label both axes with variable names and units
- Use most of the grid space when choosing your scales
Key Methods
- Plot each data pair as a point at coordinates (x, y)
- Line of best fit: draw through the "middle" of the points — roughly equal above and below
- Prediction: read from the line using the known value on one axis
- Describing correlation: state strength (strong/weak) and direction (positive/negative/none)
Key Formulas
- Correlation ≠ causation — two variables can correlate without one causing the other
- Interpolation (within range): more reliable prediction
- Extrapolation (outside range): less reliable — trend may not continue
- Line of best fit: passes through mean point (x̄, ȳ) of the data
Common Mistakes
- Correlation means causation: A strong correlation does not prove one variable causes the other
- Line of best fit through origin: Unless you can justify it, the line should follow the data — not be forced through (0, 0)
- Extrapolation described as reliable: Predictions outside the data range are less reliable — always state this
- Plotting points as connected: Scatter graphs show individual data points — do NOT join them with lines
Practice questions for Scatter Graphs
A scatter graph shows that as temperature increases, ice cream sales also increase. This is an example of:
A scatter graph shows a strong positive correlation between the number of ice creams sold and the number of drowning incidents at a beach. A student says: 'Ice cream causes drowning.' Explain why this conclusion is incorrect.