What the exam asks
- Identify explanatory and response variables from a study description and place the explanatory variable on the horizontal () axis and the response variable on the vertical () axis.
- Describe the relationship shown in a scatterplot by stating its form, direction, strength, and any unusual features, always in the context of both variables.
- Justify a claim about the relationship between two quantitative variables by citing specific features or coordinate values from the scatterplot.
Core ideas
Bivariate quantitative data and axes
Bivariate quantitative data consist of pairs of numerical measurements recorded on the same individuals or cases. Each individual appears as a single point on a scatterplot.
- Explanatory variable (-axis): The variable used to explain or predict changes in the other variable. Place it on the horizontal axis.
- Response variable (-axis): The outcome variable of interest that is predicted or explained. Place it on the vertical axis.
Describing an association: FDSU + Context
When the exam asks you to describe the relationship or describe the association in a scatterplot, a complete description covers four characteristics plus context:
| Feature | Question to ask | Standard AP vocabulary |
|---|---|---|
| Form | What overall shape do the points follow? | Linear (follows a straight-line trend) or nonlinear / curved |
| Direction | As increases, what happens to ? | Positive ( tends to increase as increases) or Negative ( tends to decrease as increases) |