A scatterplot displays pairs of numerical values $(x, y)$ as points on a coordinate plane. Each point represents one individual/case.
| Direction | Description | Example |
|---|---|---|
| Positive | As x increases, y tends to increase | Height vs weight |
| Negative | As x increases, y tends to decrease | Hours TV watched vs exam score |
| No association | No clear pattern | Shoe size vs exam score |
| Form | Description |
|---|---|
| Linear | Points follow an approximately straight-line pattern |
| Non-linear | Points follow a curved pattern (e.g. parabolic, exponential) |
How closely do the points follow the pattern?
| Strength | Description |
|---|---|
| Strong | Points cluster tightly around the pattern |
| Moderate | Some scatter around the pattern |
| Weak | Large scatter; pattern barely visible |
A point that deviates markedly from the overall pattern — either far from the main cluster or not following the trend.
“The scatterplot shows a [strong/moderate/weak], [positive/negative], [linear/non-linear] association between [x variable] and [y variable]. There [is/are / is no] outlier(s).”
Example: “The scatterplot shows a strong, positive, linear association between hours studied and exam score. There are no outliers.”
Data (hours studied, exam score):
| Hours | Score |
|---|---|
| 1 | 45 |
| 2 | 52 |
| 3 | 61 |
| 4 | 68 |
| 5 | 75 |
| 6 | 80 |
| 8 | 91 |
Plotting these points, the pattern is approximately linear, increasing from bottom-left to top-right.
Description: Strong, positive, linear association between hours studied and exam score. No outliers.
An outlier in a scatterplot is a point that:
- Falls far from the main cluster of points, or
- Does not follow the general trend (e.g. high x but low y when the trend is positive)
KEY TAKEAWAY: Outliers in a scatterplot can be misleading — always note them, then consider their effect on the regression line.
EXAM TIP: VCAA questions often give a scatterplot and ask you to describe the association. Use all four features: direction, form, strength, outliers. Missing any one feature typically costs marks.
COMMON MISTAKE: Describing only direction (“it goes up”) without mentioning strength, form, and outliers. The full description requires all four features.
