Two quantitative variables at once. Describe a scatterplot, measure the strength of a linear relationship with correlation, and model it with the least-squares regression line — then check the fit with residuals and r², and know the limits of what regression can and cannot claim.
Six ways to master Unit 5 — pick whichever fits how you like to study.
All 5 topics from the College Board CED, in order.
Unit 5 returns to two quantitative variables and asks how they move together. It begins with the scatterplot, described by its direction, form, strength, and unusual features, and with correlation r — a number between −1 and 1 that measures the strength and direction of a linear relationship (and has no units, is not resistant to outliers, and never proves causation).
The heart of the unit is the least-squares regression line (LSRL), the line that minimizes the sum of squared residuals. You'll write its equation from summary statistics or computer output, interpret its slope and y-intercept in context, use it to make predictions, and recognize the danger of extrapolation. Finally, you assess the model: a residual is observed minus predicted, a residual plot with no pattern supports a linear model, and r² tells you the proportion of variation in the response explained by the line — while influential points can pull the whole model.
This unit is 10–20% of the AP Statistics exam and takes about 9 class periods. The four statistical practices below run through every topic: