"Man does not live by a correlation alone." You always need to look at a scatter plot of the data as well. (Neither is foolproof by itself.) You conduct a study to see whether the amount of time spent studying per week is related to GPA for a group of college computer science majors.

## Sample questions

How do you designate the "time spent studying" variable on a scatter plot of your data?

**Answer:**the*X*variableThe logical assumption in this study is that time spent studying influences grades (GPA), so it makes sense to designate "time spent studying" as the

*X,*or explanatory, variable.How do you designate the variable "GPA" on a scatter plot of your data?

A. the

*X*variableB. the

*Y*variableC. the response variable

D. Choices (A) and (C)

E. Choices (B) and (C)

**Answer: E.**Choices (B) and (C) (the*Y*variable; the response variable)The logical assumption in this study is that time spent studying influences GPA, so it's logical to designate "GPA" as the

*Y,*or response, variable.How does the correlation change if you switch the measurement of study time from minutes to hours?

**Answer:**It doesn't change.The correlation is a unitless measure, so changing the units in which variables are measured won't change their correlation.

How does the correlation change if you switch the designation of the two variables — that is, make the

*X*variable the*Y*variable and make the*Y*variable the*X*variable?**Answer:**It doesn't change.In a correlation, it doesn't matter which variable is designated as

*X*and which as*Y;*the correlation will be the same either way.

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