Variables and Study Design

1.  A survey of 100 students in Orange County Community College was taken to see how they preferred to study.  The survey showed that 38 students liked it quiet, 20 students liked the television on, 34 students liked the stereo on, and 8 students liked white noise (as in a lunch room).  

a)  Identify the variable of interest.

b)  Is the variable quantitative or qualitative?

c)  What is the implied population? Be specific. 

d)  What is the sample? 

2.  Ecology Wetlands:  The clean Water Act was passed by Congress more than 30 years ago.  Since then, government agencies have carefully monitored water quality and its effect on wetlands.  (Reference:  Environmental Protection Agency Wetland Report EPA 832-R-93-005).  Of particular concern is the concentration of nitrogen in water draining from fertilized lands.  Too much nitrogen can kill fish and wildlife.  Suppose a student intern working for the Environmental Protection Agency has been studying the nitrogen concentration in a lake receiving drainage from a local golf course.  Twenty-eight samples of water were taken at random from the lake.  The nitrogen concentration (milligrams of nitrogen per liter of water) was determined for each sample.  

a)  Identify the variable.

b)  Is the variable quantitative or qualitative?

c)  What is the sample? 

d)  What is the implied population?

3.  Fireflies:  Suppose you are conducting a study to compare firefly populations exposed to normal daylight/darkness conditions with firefly populations exposed to continuous light (24 hours a day).  You set up two colonies in a laboratory environment.  The two colonies are identical except that one colony is exposed to normal daylight/darkness conditions and the other is exposed to continuous light.  Each colony is populated with the same number of mature fireflies.  After 72 hours, you count the number of living fireflies in each colony.  

a)  What is the goal of this study?  

b)  Is this an experiment or an observation study?  Explain. 

c)  Identify the treatment group.

d)  Identify the control group. 

4. Classify each variable as qualitative or quantitative. 

a)  Colors of automobiles in the faculty parking lot.

b)  Number of desks in a classroom.

c)  Weights of fish caught in Lake Tahoe.

d)  Capacity in gallons of water in selected dams.

5.  Classify each variable as discrete or continuous. 

a)  Lifetime of batteries in a tape recorder.

b)  Weights of newborn infants at a certain hospital.

c)  Number of students each day who make appointments with a math tutor at the tutoring center   

Question 2

6.  For the information that follows, list the highest level of measurement that should be used: nominal, ordinal, interval, or ratio.  

A restaurant manager is developing a clientele profile.  Some of the information for the profile are as follows.  

a)  Gender of diners

b)  Size of groups (number of people) dining together

c)  Time of day the last diner of the evening departs

d)  Age grouping:  young, middle age, senior 

e)  Length of time a diner waits for a table

7.  Student Life:  Categorize these measurements associated with student life according to level: nominal, ordinal, interval, or ratio.  

a)  Length of time to complete an exam 

b)  Major field of study 

c)  Number of credits taken 

d)  Course evaluation: poor acceptable, good

e)  Score on last exam (based on 100 possible points)

8.  You want to know the “average annual salary” of registered nurses in Washington State.    

a)  Who are the individuals (population) in this study.

b)  Identify the main variable of the study.  Classify this variable as quantitative or qualitative.   

Main Variable:

Is the main variable quantitative or qualitative?  

c)  Identify 3 other variables that are relevant to this study.

9.   Identify the sample and the population.  Also, determine whether the sample is likely to be representative of the population. 

a)  A reporter for Newsweek stands on a street corner and asks 10 adults if they feel that the current 

U.S. president is doing a good job. 

Population: 

Sample:    

Is the sample representative of the population?   YES       NO 

Explain your answer:

b)  Nielsen Media Research surveys 5000 randomly selected households and finds that among the TV 

sets in use, 19% are tuned to 60 Minutes (based on data from USA Today).   

Population: 

Sample:    

Is the sample representative of the population?   YES       NO 

Explain your answer:

11.  Subjects are randomly assigned to four groups.  Each group is placed on one of four special diets: a low-fat diet, high-fish diet, combination of low-fat and high-fish diet, and regular diet.   After 6 months, the blood pressures of the groups are compared to see if diet has any effect on blood pressure.  

a)  Classify this study (circle the answer):    experimental  OR  observational 

b)  Identify the independent variable:

c)  Identify the dependent variable:

d)  Describe the goal of this study.

12. People who walked at least 3 miles a day are randomly selected and their blood triglyceride levels are measured in order to determine if the number of miles that they walk has any influence on these levels.   

a)  Classify this study (circle the answer):    experimental OR  observational 

b)  Identify the independent variable:

c)  Identify the dependent variable:

d)  Describe the goal of this study. 

13.  Subjects were randomly assigned to two groups.  One group was given an herb and the other group a placebo.  After 6 months the numbers of respiratory tract infections each group had were compared.  

a)  Classify this study (circle the answer):    experimental OR  observational 

b)  Identify the treatment group.

c)   Identify the independent variable.

d)  Identify the dependent variable.

e) What is the goal of this study?