Two-Variable Data • Topic 1 of 5

Scatterplots

A scatterplot plots paired measurements as points, one variable on each axis, to reveal how the two relate. The overall direction shows the kind of association: points sloping up to the right are a positive association, down to the right a negative association, and a shapeless cloud means no association. How tightly the points cluster around a straight line shows the strength — close to the line is strong, widely spread is weak. Reading a scatterplot means describing both direction and strength together, for example “a strong positive association,” which is exactly what the SAT asks you to identify.

Scatterplot of ten data points with a mild upward trendScatterplotxyEach dot is one (x, y) data pair.

✅ Solved examples

1. Points slope up to the right, close to a line. Describe the association.
Upward and tight: a strong positive association.
2. Points slope down to the right but are loosely spread. Describe it.
Downward and loose: a weak negative association.
3. Points form a shapeless cloud. What association is there?
No clear direction means no association.
4. Points slope up but scatter widely. Strength?
Upward but spread out: weak positive.

✏️ Practice — try these, take hints as needed

1. Points rise to the right and lie very close to a line. Describe it.
Direction then strength.
Up + tight.
—
Strong positive association.
2. Points fall to the right and hug a line. Describe it.
Down + tight.
—
—
Strong negative association.
3. Points show no pattern at all. Association?
No direction.
—
—
No association.
4. Points drift downward but are widely scattered. Describe it.
Down + loose.
—
—
Weak negative association.
5. Points rise to the right, moderately spread. Direction?
Upward.
—
—
Positive.

📝 Topic test — 8 questions

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