A nutritionist collects data from 25 popular breakfast cereals. For each cereal, the number of calories per serving is plotted on the x-axis against the number of milligrams of sodium on the y-axis. The value of r for the resulting scatterplot is 0.83. How would the value of the correlation coefficient, r, change if sodium was plotted on the x-axis and calories plotted on the y-axis?
Answer
A
The value of r would increase.
B
The value of r would not change.
C
The value of r would change to –0.83.
D
The value of r could increase or decrease, depending of the strength of the new relationship.
Explanation
The correlation coefficient is unchanged when the x- and y-variables are switched. It describes the direction and strength of the linear relationship, not which variable is plotted on which axis. Therefore, plotting sodium against calories instead of calories against sodium leaves r at 0.83, so the value would not change.
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