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MathidiaMathematics Academy
Statistics and data
Lesson 64 of 75
Challenge

Scatter graphs

Objective. Describe correlation and use lines of best fit cautiously.

  1. 1. Learn
  2. 2. Worked example
  3. 3. Practice
  4. 4. Feedback
  5. 5. Continue

Learn: the key idea

A scatter graph plots pairs of related values as points to reveal correlation, showing whether two variables tend to increase together (positive correlation), one increases as the other decreases (negative correlation), or show no clear pattern at all. A line of best fit is drawn through the general trend of the points, balancing them roughly evenly on each side, and can be used to estimate values between known data points. Using it to estimate far beyond the plotted data, called extrapolation, is unreliable since the trend may not continue. Example: if height and shoe size show positive correlation, a line of best fit could estimate shoe size for an untested height within the sampled range.

Worked example

A scatter graph of ice cream sales against temperature shows points rising steadily from bottom-left to top-right. Describe the correlation shown by the scatter graph.

Options
  • Positive correlation
  • Negative correlation
  • No correlation
  • Zero correlation
  1. 1Observe the general direction of the plotted points on the graph.
  2. 2Points rising from bottom-left to top-right indicate both variables increasing together.
  3. 3This pattern matches the definition of positive correlation.
  4. 4The scatter graph shows positive correlation between temperature and ice cream sales.

Answer: Positive correlation

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Common mistake. Pupils often join points up dot-to-dot instead of drawing one straight line of best fit showing the overall trend; the line should balance scattered points evenly, not pass through every one.

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