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8th grade · Math · Unit 6 of 17

Scatter Plots & Stories

Two-variable data and misleading graphs

What your child practices

Deciding when two-variable data is needed, picking the best graph, describing scatter plots as strong, weak, positive, negative or none, spotting outliers, and noticing graphs that mislead.

Alaska content standards learning standard: 8.SP.1; 8.SP.2 · scatter plots and patterns of association

How we explain it

Children can open this short lesson before they practice.

  1. A scatter plot shows two sets of data as points.
  2. Points that rise together show a positive relationship.
  3. A point far from the pattern is an outlier.

Example: As study time goes up, test scores go up. What kind of relationship is that? Both values rise together. That is a positive relationship. Answer: Positive

Scatter Plots & Stories in Alaska

In the Alaska content standards, this is unit 6 of 17 in 8th grade Math, after Big, Small & Real Numbers and before Tessellations & Transformations.

Gradelings describes a child's practice on this unit as Beginning, Approaching, Meeting or Exceeding (Four practice steps). That reflects practice, not a report-card mark: the teacher decides the mark.

Source: Alaska Department of Education and Early Development

Sample questions

A taste of this unit. In the app, questions change every time and get easier or harder to match your child.

  1. Question 1

    Which variable is continuous?

    • the height of a plant
    • the number of leaves on a plant
    • the number of plants on a shelf
    • the number of flowers that open

  2. Question 2

    All of the points but one lie on a line. Which point is the outlier?

    Points on a scatter plot
    xy
    15
    29
    331
    417
    521
    625
    • (2, 9)
    • (4, 17)
    • (3, 31)
    • (1, 5)

  3. Question 3

    A bar graph's vertical axis starts at 90 instead of 0. What effect can this have?

    • Large differences look smaller than they are.
    • Small differences look much larger than they are.
    • The bars become impossible to compare.
    • It has no effect on how the graph looks.

  4. Question 4

    Every graph should show…

    • only the data points
    • the most colorful design
    • the largest values at the left
    • a title, labeled axes, a suitable scale and a source

  5. Question 5

    On a scatter plot, as the x-values increase, the y-values go up too. The points are loosely scattered around a line. How would you describe the relationship?

    • strong positive
    • weak negative
    • weak positive
    • strong negative

  6. Question 6

    Which graph is best for showing how height and arm span are related for 30 students?

    • a circle graph
    • a scatter plot
    • a pictograph
    • a bar graph of the heights only

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