Choosing Appropriate Scales for Scatter Plot Axes
Choosing Appropriate Scales for Scatter Plot Axes is a Grade 7 math skill in Big Ideas Math Advanced 2, Chapter 9: Data Analysis and Displays, where students select axis scales that allow all data points to be plotted clearly without wasting space, by analyzing the range of each variable and choosing consistent intervals. Good scale selection is essential for revealing true patterns and avoiding visual distortions.
Key Concepts
When creating a scatter plot, choose scales that: (1) include all data values with some space beyond the minimum and maximum, (2) use convenient intervals that make the graph easy to read, and (3) result in a plot that uses most of the available space without being cramped or too spread out.
Common Questions
How do you choose an appropriate scale for a scatter plot axis?
Find the minimum and maximum values of the variable for that axis. Choose a starting point at or slightly below the minimum and an ending point at or above the maximum. Select equal intervals that divide the range into 4-8 manageable steps.
What happens when the scale is too compressed or too spread out?
A compressed scale (large intervals) can make all points appear clustered together, hiding patterns. A spread-out scale (tiny intervals) makes the graph too large and hard to read. Both can misrepresent the data.
Does the scale need to start at zero?
Not always. If all data values are far from zero, you can start the axis near the minimum value to spread the data more clearly. A break symbol is sometimes used to show the axis does not start at zero.
What is Big Ideas Math Advanced 2 Chapter 9 about?
Chapter 9 covers Data Analysis and Displays, including constructing scatter plots, choosing appropriate scales, identifying associations, drawing lines of best fit, and interpreting two-variable data.