Learning outcomes
- define a scatterplot
- plot paired numerical data points
- identify direction and pattern visually
- distinguish scatterplot from other graph types
What is a scatterplot?
- A scatterplot shows paired values of two numerical variables as points.
- Each point represents one case.
- x-axis: study hours
- y-axis: marks
(5, 78) means one student studied 5 hours and scored 78.
Why scatterplots are useful
- They reveal:
- direction
- strength
- form
- unusual points
Basic reading questions
- Do points rise from left to right?
- Do points fall from left to right?
- Are points tightly grouped or widely scattered?
- Is the pattern roughly straight or curved?
Exam hints and traps
- Scatterplot is only for paired numerical data.
- One point corresponds to one observation pair.
- A scatterplot may show no clear pattern at all.
- Do not treat category labels as scatterplot axes.
Quick practice
- Can a scatterplot be used for blood group and marks?
- What does one point represent?
- If points generally rise from left to right, what kind of direction is suggested?
Answer key
- No, because blood group is categorical
- One pair of numerical observations
- Positive direction