Scatterplots on the SAT
Trend, Association, and Predictions
Build equations from context, spot patterns fast, and practice with intent.
Why the SAT Emphasizes Scatterplots
Scatterplots show how two variables move together. The SAT asks you to describe the trend, identify whether the association is positive or negative, and sometimes make a prediction using a line of best fit.
This lesson shows how to read the overall pattern rather than chasing individual points. You will learn how to estimate a trend line and how to explain what a slope means in context.
A Simple Definition Unlocks Scatterplots
A positive association means the points rise as you move right. A negative association means the points fall. If the points are scattered with no clear direction, there is no association.
The line of best fit is a simple model, not an exact rule. It should cut through the middle of the points, with roughly equal points above and below. Use it to make estimates, not exact predictions.
Work Through Scatterplots Step by Step
Using points $(1, 2)$ and $(8, 8)$, estimate $y$ when $x = 5$ from a line of best fit.
Estimate a value using a line of best fit, and explain why it is an approximation.
Use the line through $(1, 2)$ and $(8, 8)$
Simplify the slope to a reduced fraction.
Estimate at $x = 5$
Compute the result to simplify the expression.
Use Desmos to Check Scatterplots
Using points $(1, 2)$ and $(8, 8)$, estimate $y$ when $x = 5$ from a line of best fit.
Desmos makes scatterplots and regression lines fast. Enter the data in a table and use regression to get the best fit line.
y_1 ~ m x_1 + b
Algebra is fine for estimating from two points. Desmos is faster with many data points.
Expert move: Enter $x_1$ and $y_1$ in a table to plot the scatterplot, then
use a regression command like y1 ~ m x1 + b when you need the line of best fit.
Check yourself: Desmos can compute the line, but you still have to interpret correlation, outliers, and context.
- Desmos features used: tables, regression.
- Common mistake: confusing correlation with causation.
Practice Scatterplots with SAT-Style Questions
Interpret trends and predictions.
A scatterplot shows points trending upward from left to right. What type of association is this?
A line of best fit has slope . What does that mean?
Which point is an outlier in a set where most points follow ?
Using a line of best fit , estimate when .
Key Takeaways to Remember for Scatterplots
- Positive association rises, negative association falls.
- Outliers are points far from the overall trend.
- Desmos regression is fast for large data sets.
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