The correlation coefficient r, and correlation is not causation

Grade 9 Math Worksheet

Circle the best answer.

1. 1.

   Jun plotted mistakes in a song against daily practice time. The calculator gives r = -0.97. Which sentence describes the association?

   • Weak and positive: the number of mistakes tends to go up a little, with lots of scatter.
   • Strong and negative: as the practice time goes up, the number of mistakes tends to go down.
   • Strong and positive: as the practice time goes up, the number of mistakes tends to go up a lot.
   • Weak and negative: the number of mistakes tends to go down a little, with lots of scatter.
2. 2.

   Luz plotted sprouted seeds against seeds planted. The calculator gives r = 0.97. Which sentence describes the association?

   • Strong and negative: as the number of seeds planted goes up, the number that sprouted tends to go down.
   • Weak and negative: the number that sprouted tends to go down a little, with lots of scatter.
   • Strong and positive: as the number of seeds planted goes up, the number that sprouted tends to go up.
   • Weak and positive: the number that sprouted tends to go up a little, with lots of scatter.
3. 3.

   Milo plotted hats in the lost and found against the temperature. The calculator gives r = -0.34. Which sentence describes the association?

   • Weak and positive: the number of hats tends to go up a little, with lots of scatter.
   • Weak and negative: the number of hats tends to go down a little, with lots of scatter.
   • Strong and positive: as the temperature goes up, the number of hats tends to go up.
   • Strong and negative: as the temperature goes up, the number of hats tends to go down a lot.
4. 4.

   Pia made two plots: Set A, cocoa sales by temperature, has r = -0.98. Set B, lemonade sales by temperature, has r = 0.54. Which set shows the stronger linear association?

   • Set B, because a positive r is stronger than a negative one.
   • Set A, because -0.98 is closer to -1 than 0.54 is to 1.
   • They are equally strong.
   • Set B, because 0.54 is greater than -0.98.
5. 5.

   Ren made two plots: Set A, lemonade sales by temperature, has r = 0.71. Set B, sprouts by seeds planted, has r = 0.98. Which set shows the stronger linear association?

   • Set B, because 0.98 is closer to 1 than 0.71.
   • They are equally strong.
   • Set A, because its line is steeper.
6. 6.

   Tala made two plots: Set A, paper airplane flights by wing width, has r = 0.97. Set B, kite heights by wind speed, has r = 0.69. Which set shows the stronger linear association?

   • Set A, because 0.97 is closer to 1 than 0.69.
   • They are equally strong.
   • Set B, because its line is steeper.
7. 7.

   Zee plotted beach-shop sunglasses sales against lemonade sales. The calculator gives r = 0.97. Which is the best explanation for the link?

   • Drinking lemonade makes people buy sunglasses.
   • A third thing, hot, sunny weather, tends to push both up.
   • r = 0.97 is so close to 1 that one must cause the other one.
   • Buying sunglasses makes people buy lemonade.
8. 8.

   Ari plotted mittens in the lost and found against soup sold. The calculator gives r = 0.97. Which is the best explanation for the link?

   • A third thing, cold weather, tends to push both up.
   • Buying soup makes students lose mittens.
   • r = 0.97 is so close to 1 that one must cause the other.
   • Losing mittens makes students buy soup.
9. 9.

   Bo plotted spelling scores against foot length for students in grades 1 to 5. The calculator gives r = 0.96. Which is the best explanation for the link?

   • r = 0.96 is so close to 1 that one must cause the other.
   • Spelling well makes feet grow.
   • A third thing, age, tends to push both up.
   • Longer feet make students better spellers.
10. 10.

    Esme plotted library books checked out against umbrellas in the stand. The calculator gives r = 0.91. Which is the best explanation for the link?

    • A third thing, rainy weather, tends to push both up.
    • Borrowing books makes students bring umbrellas.
    • Umbrellas in the stand make students borrow books.
    • r = 0.91 is so close to 1 that one must cause the other.