8th grade · Math · Unit 6 of 19
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.
New York State Learning Standards learning standard: NY-8.SP.1; NY-8.SP.2 · scatter plots and patterns of association
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 New York
In the New York State Learning Standards, this is unit 6 of 19 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
Which best describes the relationship between the age of a used car and its price?
- no relationship
- a negative relationship
- a positive relationship
a negative relationship
Hint: Ask: as one goes up, what does the other tend to do? If nothing, there is no relationship.
Question 2
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?
- weak negative
- strong 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 3
Which graph is best for comparing the number of students in each club?
- a bar graph
- a circle graph with no percents
- a line graph
- a scatter plot
a bar graph
Hint: A bar graph compares amounts for separate categories.
Question 4
The points on a scatter plot are spread out with no pattern. How would you describe the relationship?
- weak positive
- none
- strong positive
- strong negative
none
Hint: If one variable does not predict the other, there is no relationship.
Question 5
What is the purpose of an infographic?
- to replace the data collection
- to list raw data with no explanation
- to tell a story about data using tables, graphs and images
- to hide small values
to tell a story about data using tables, graphs and images
Hint: An infographic combines visuals and text to communicate the main message.
Question 6
A pictograph shows twice as many sales using a picture twice as wide and twice as tall. Why is this misleading?
- The picture's area is four times as large, so it looks like more than double.
- Twice as wide always means twice as many.
- The picture is the wrong shape.
- Pictographs cannot show sales.
The picture's area is four times as large, so it looks like more than double.
Hint: Doubling both width and height multiplies the area by 4.