How it works
This scatter plot and trend line worksheet has 36 questions: name the correlation in a set of points, predict with a trend line and read its slope, choose the line that fits best, and outliers, r and causation.
Read the full guide
Four sets
Describe the correlation gives six points and asks positive, negative or none. Use a trend line predicts values and explains slope and intercept. Best-fitting line compares four equations. Scatter plot words covers outliers, r, interpolation and causation.
Print or practise
Practice brings a missed question back until you get it right. The sheet on screen is what prints: remove a question, add more up to all 36, and tick With answer key.
- Read left to right: rising points are a positive correlation, falling points negative.
- To predict, put the x value into the trend line equation and work out y.
- The sign of r gives the direction; its size gives the strength.
Questions and answers
How do you draw a trend line on a scatter plot?
Draw a straight line that follows the direction of the points, with about as many points above it as below. The least-squares line of best fit makes the total squared vertical distance as small as possible.
What are the three types of correlation?
Positive (y rises as x rises), negative (y falls as x rises) and no correlation (no straight-line pattern). The correlation coefficient r runs from −1 to 1.
Does correlation mean causation?
No. Two things can rise together because a third thing drives both: ice cream sales and sunburns both go up in hot weather.