Question 1049220: Examining Relationships
Question 3
Select one answer.
10 points
If there is no relationship (linear or otherwise) between two quantitative variables as observed on a scatterplot, the value of the correlation coefficient, r, is likely to be which of the following?
Closer to 1
Closer to −1
Closer to 0
Either closer to −1 or 1
Question 4
Select one answer.
10 points
Using data from 100 hospitals, a correlation of r = 0.78 is found between the size of a hospital (measured in number of beds) and the average length of patient stays (measured in days). Which of the following is true?
There is a pretty strong positive linear correlation between number of beds and length of hospital stay.
Severity of illness is a possible lurking variable that is behind this relationship.
Increasing hospital size must be the cause of longer patient stays.
Question 6
Select one answer.
10 points
Suppose the correlation between two variables (x, y) in a data set is determined to be r = 0.63, What must be true about the slope, b, of the least-squares line estimated for the same set of data?
The slope b is always equal to the square of the correlation r.
The slope will have the opposite sign as the correlation.
The slope will have the same sign as the correlation.
The slope will also be a value between −1 and 1.
Question 7
Select all that apply.
10 points
A study was done on the timeliness of flights categorized as either "on time" or "delayed" of two major airlines: StatsAir and AirMedian. Data were collected over a period of time from five major cities and it was found that StatsAir does better overall (i.e., has a smaller percentage of flights categorized as delayed). However, in each of the five cities separately, AirMedian does better (i.e., has a smaller percentage of flights categorized as delayed in each city).
Which of the following is correct? Check all that apply.
This is an example of Simpson's paradox.
"City" is a lurking variable in this example.
This is an example of a negative association between variables.
Question 8
Select one answer.
10 points
A correlation of r = 0.85 is found between weekly sales of firewood and cough drops over a 1-year period. Which of the following is a correct interpretation of this correlation value?
Temperature is a possible lurking variable that is behind this relationship.
There is a pretty strong positive linear relationship between sales of firewood and cough drops.
Fire must be the cause of coughing.
Answer by ikleyn(52788)   (Show Source):
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