a.
To identify: A possible lurking variable.
The lurking variable is the patient’s condition.
Given information:
The association between x and y might be due to a third variable z that influences both x and y . If such a variable is not part of the study model, it is called a lurking variable.
There is a positive association between the size of a hospital and the death rate among its patients.
Explanation:
The size of the hospital is not affecting the death rates of the patients. The lurking variable is the patient’s condition.
It is more likely that the bigger hospitals tend to get the more critical cases, and critical cases have a higher death rate.
b.
To identify: A possible lurking variable.
The lurking variable is the size of the aircraft.
Given information:
The association between x and y might be due to a third variable z that influences both x and y . If such a variable is not part of the study model, it is called a lurking variable.
There is a positive association between the number of seats on a commercial jet and the speed at which the aircraft travels.
Explanation:
The number of seats does not affect the speed of the jet. The lurking variable is the size of the aircraft. Larger jets usually have more seats and go faster.
c.
To identify: A possible lurking variable.
The lurking variable is the age of the student.
Given information:
The association between x and y might be due to a third variable z that influences both x and y . If such a variable is not part of the study model, it is called a lurking variable.
There is a positive association between shoe size and reading level among elementary school students.
Explanation:
The size of the shoe does not affect reading ability. The lurking variable is the age of the student. In general, older students have larger feet and read at a higher level.
d.
To identify: A possible lurking variable.
The lurking variable is the size of the fire.
Given information:
The association between x and y might be due to a third variable z that influences both x and y . If such a variable is not part of the study model, it is called a lurking variable.
There is a positive association between the number of firemen fighting a fire and the amount of damage that the fire causes.
Explanation:
The extra firemen are not causing more damage. The lurking variable is the size of the fire. Larger fires cause more damage and require more firefighters.
e.
To identify: A possible lurking variable.
The lurking variable is the player’s position on the team.
Given information:
The association between x and y might be due to a third variable z that influences both x and y . If such a variable is not part of the study model, it is called a lurking variable.
Among professional football players there is a negative association between body weight and annual income.
Explanation:
The salary depends on the skills of the player. The lurking variable is the player’s position on the team.
Chapter 10 Solutions
PRECALCULUS:GRAPHICAL,...-NASTA ED.
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