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.
Alabama Course of Study content standard: 8.18; 8.19 · scatter plots, patterns of association and lines of fit
How we explain it
Children can open this short lesson before they practice.
- A scatter plot shows two sets of data as points.
- Points that rise together show a positive relationship.
- 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 Alabama
In the Alabama Course of Study, 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.
Sample questions
A taste of this unit. In the app, questions change every time and get easier or harder to match your child.
Question 1
The points on a scatter plot are spread out with no pattern. How would you describe the relationship?
- none
- strong positive
- strong negative
- weak positive
none
Hint: If one variable does not predict the other, there is no relationship.
Question 2
A graph has no title and no labels on its axes. What is the problem?
- The graph must be a scatter plot.
- Readers cannot tell what the data shows.
- Nothing, because the shape tells the story.
- The data must be wrong.
Readers cannot tell what the data shows.
Hint: A good graph has a title, labels, units and a source.
Question 3
All of the points but one lie on a line. Which point is the outlier?
Points on a scatter plot x y 1 8 2 11 3 -1 4 17 5 20 6 23 - (3, −1)
- (1, 8)
- (4, 17)
- (2, 11)
(3, −1)
Hint: An outlier does not fit the pattern of the other points. Find the point that is far from the line the others make.
Question 4
On a scatter plot, as the x-values increase, the y-values go up too. The points lie very close to a line. How would you describe the relationship?
- strong negative
- weak negative
- weak positive
- strong positive
strong positive
Hint: Positive means both go up together; negative means one goes up as the other goes down. Strong means the points are close to a line.
Question 5
A student collects data on hours of practice and number of free throws made. Which graph best shows whether the two are related?
- a pictograph
- a circle graph
- a bar graph with one bar
- a scatter plot
a scatter plot
Hint: Two numerical variables measured for each person fit a scatter plot.
Question 6
Which question needs two-variable data?
- How does a plant's height change with the hours of sunlight it gets?
- What is each student's favorite lunch?
- How many students ride the bus each day?
How does a plant's height change with the hours of sunlight it gets?
Hint: One-variable data describes one thing for each person or object. Two-variable data pairs two measurements to look for a relationship.