Question

Vocabulary How can you use a trend line to determine the type
of linear association for a scatter plot? Lesson 4-2

Answer 1

A trend line (line of best fit) shows the overall direction of points in a scatter plot so you can tell both the direction and strength of a linear association.

How to use it:
- Draw or fit the trend line through the points so most points are close to it.
- Direction:
- If the trend line slopes upward left-to-right → positive linear association (as x increases, y tends to increase).
- If it slopes downward left-to-right → negative linear association (as x increases, y tends to decrease).
- If it is nearly horizontal → little or no linear association (y does not change much with x).
- Strength:
- If the points lie close to the trend line → strong linear association.
- If the points are widely scattered around the line → weak linear association.
- Caveats:
- A near-horizontal trend line means no linear association but there could still be a non‑linear relationship.
- Outliers can distort the trend line, so check for them.

(You can also compute the correlation coefficient r: r near +1 is strong positive, near −1 is strong negative, and near 0 indicates little or no linear association.)