Chapter 4: Scatterplots and Correlation

Question 1

Scatterplot

Answer 1

-Shows relationship between 2 quantitative variables measured on the same individuals

Question 2

Linear relationship

Answer 2

• Points of a scatterplot tend to fall along/near a straight line
• Slope=constant, easy to describe

Question 3

Positive relationship

Answer 3

• Above average values of both variables to to occur together, same w/below average
• Upward sloping pattern

Question 4

Negative relationship

Answer 4

• Above average values of one variable tend to accompany below average values of the other, vice-versa
• Downward sloping pattern

Question 5

The Correlation Coefficient (r)

Answer 5

• Measures how closely a straight line fits the pts in a scatterplot
• Measures strength of linear relationship between variables

Question 6

Properties of Correlation Coefficient

Answer 6

• Both variables must be quantitative
• A perfect + linear relationship would be +1
• A perfect - linear relationship would be -1
• No linear relationship would be 0
• Doesn’t distinguish between response and explanatory variables (correlation doesn’t equal causation)
• Has no units, changing units has no effect on r
• Outlier sensitive (can decrease or increase/confirm correlation)