# Homework

### 1.1 Definitions of Statistics, Probability, and Key Terms

For each of the following situations, indicate whether it would be best modeled with a mathematical model or a statistical model. Explain your answers.

- driving time from New York to Florida
- departure time of a commuter train at rush hour
- distance from your house to school
- temperature of a refrigerator at any given time
- weight of a bag of rice at the store

*For each of the following eight exercises, identify: *

*a. the population, b. the sample, c. the parameter, d. the statistic, e. the variable, and f. the data. Give examples where appropriate.*

A fitness center is interested in the mean amount of time a client exercises in the center each week.

Ski resorts are interested in the mean age that children take their first ski and snowboard lessons. They need this information to plan their ski classes optimally.

A cardiologist is interested in the mean recovery period of her patients who have had heart attacks.

Insurance companies are interested in the mean health costs each year of their clients, so that they can determine the costs of health insurance.

A politician is interested in the proportion of voters in his district who think he is doing a new good job.

A marriage counselor is interested in the proportion of clients she counsels who stay married.

Political pollsters may be interested in the proportion of people who will vote for a particular cause.

A marketing company is interested in the proportion of people who will buy a particular product.

*Use the following information to answer the next three exercises:*

A Lake Tahoe Community College instructor is interested in the mean number of days Lake Tahoe Community College math students are absent from class during a quarter.

What is the population she is interested in?

- all Lake Tahoe Community College students
- all Lake Tahoe Community College English students
- all Lake Tahoe Community College students in her classes
- all Lake Tahoe Community College math students

Consider the following:

$X$ = number of days a Lake Tahoe Community College math student is absent.

In this case, *X* is an example of which of the following?

- variable
- population
- statistic
- data

The instructor’s sample produces a mean number of days absent of 3.5 days. This value is an example of which of the following?

- parameter
- data
- statistic
- variable

### 1.2 Data, Sampling, and Variation in Data and Sampling

*For the following exercises, identify the type of data that would be used to describe a response (quantitative discrete, quantitative continuous, or qualitative), and give an example of the data:*

number of tickets sold to a concert

percent of body fat

favorite baseball team

time in line to buy groceries

number of students enrolled at Evergreen Valley College

most-watched television show

brand of toothpaste

distance to the closest movie theatre

age of executives in Fortune 500 companies

number of competing computer spreadsheet software packages

*Use the following information to answer the next two exercises:*

A study was done to determine the age, number of times per week, and the duration (amount of time) of resident use of a local park in San Jose. The first house in the neighborhood around the park was selected randomly and then every 8th house in the neighborhood around the park was interviewed.

*Number of times per week* is what type of data?

- qualitative
- quantitative discrete
- quantitative continuous

*Duration (amount of time)* is what type of data?

- qualitative
- quantitative discrete
- quantitative continuous

Airline companies are interested in the consistency of the number of babies on each flight, so that they have adequate safety equipment. Suppose an airline conducts a survey. Over Thanksgiving weekend, it surveys six flights from Boston to Salt Lake City to determine the number of babies on the flights. It determines the amount of safety equipment needed by the result of that study.

- Using complete sentences, list three things wrong with the way the survey was conducted.
- Using complete sentences, list three ways that you would improve the survey if it were to be repeated.

Suppose you want to determine the mean number of students per statistics class in your state. Describe a possible sampling method in three to five complete sentences. Make the description detailed.

Suppose you want to determine the mean number of cans of soda drunk each month by students in their twenties at your school. Describe a possible sampling method in three to five complete sentences. Make the description detailed.

List some practical difficulties involved in getting accurate results from a telephone survey.

List some practical difficulties involved in getting accurate results from a mailed survey.

With your classmates, brainstorm some ways you could overcome these problems if you needed to conduct a phone or mail survey.

The instructor takes her sample by gathering data on five randomly selected students from each Lake Tahoe Community College math class. The type of sampling she used is which of the following?

- cluster sampling
- stratified sampling
- simple random sampling
- convenience sampling

A study was done to determine the age, number of times per week, and the duration (amount of time) of residents using a local park in San Jose. The first house in the neighborhood around the park was selected randomly and then every eighth house in the neighborhood around the park was interviewed. The sampling method was which of the following?

- simple random
- systematic
- stratified
- cluster

Name the sampling method used in each of the following situations:

- A woman in the airport is handing out questionnaires to travelers asking them to evaluate the airport’s service. She does not ask travelers who are hurrying through the airport with their hands full of luggage, but instead asks all travelers who are sitting near gates and not taking naps while they wait.
- A teacher wants to know if her students are doing homework, so she randomly selects rows two and five and then calls on all students in row two and all students in row five to present the solutions to homework problems to the class.
- The marketing manager for an electronics chain store wants information about the ages of its customers. Over the next two weeks, at each store location, 100 randomly selected customers are given questionnaires to fill out asking for information about age, as well as about other variables of interest.
- The librarian at a public library wants to determine what proportion of the library users are children. The librarian has a tally sheet on which she marks whether books are checked out by an adult or a child. She records this data for every fourth patron who checks out books.
- A political party wants to know the reaction of voters to a debate between the candidates. The day after the debate, the party’s polling staff calls 1,200 randomly selected phone numbers. If a registered voter answers the phone or is available to come to the phone, that registered voter is asked whom he or she intends to vote for and whether the debate changed his or her opinion of the candidates.

A *random survey* was conducted of 3,274 people of the *microprocessor generation*—people born since 1971, the year the microprocessor was invented. It was reported that 48 percent of those individuals surveyed stated that if they had $2,000 to spend, they would use it for computer equipment. Also, 66 percent of those surveyed considered themselves relatively savvy computer users.

- Do you consider the sample size large enough for a study of this type? Why or why not?
- Based on your
*gut feeling*, do you believe the percents accurately reflect the U.S. population for those individuals born since 1971? If not, do you think the percents of the population are actually higher or lower than the sample statistics? Why?Additional information: The survey, reported by Intel Corporation, was filled out by individuals who visited the Los Angeles Convention Center to see the Smithsonian Institute's road show called “America’s Smithsonian.”

- With this additional information, do you feel that all demographic and ethnic groups were equally represented at the event? Why or why not?
- With the additional information, comment on how accurately you think the sample statistics reflect the population parameters.

The Well-Being Index is a survey that follows trends of U.S. residents on a regular basis. There are six areas of health and wellness covered in the survey: Life Evaluation, Emotional Health, Physical Health, Healthy Behavior, Work Environment, and Basic Access. Some of the questions used to measure the Index are listed below.

Identify the type of data obtained from each question used in this survey: qualitative, quantitative discrete, or quantitative continuous.

- Do you have any health problems that prevent you from doing any of the things people your age can normally do?
- During the past 30 days, for about how many days did poor health keep you from doing your usual activities?
- In the last seven days, on how many days did you exercise for 30 minutes or more?
- Do you have health insurance coverage?

In advance of the 1936 presidential election, a magazine released the results of an opinion poll predicting that the republican candidate Alf Landon would win by a large margin. The magazine sent post cards to approximately 10,000,000 prospective voters. These prospective voters were selected from the subscription list of the magazine, from automobile registration lists, from phone lists, and from club membership lists. Approximately 2,300,000 people returned the postcards.

- Think about the state of the United States in 1936. Explain why a sample chosen from magazine subscription lists, automobile registration lists, phone books, and club membership lists was not representative of the population of the United States at that time.
- What effect does the low response rate have on the reliability of the sample?
- Are these problems examples of sampling error or nonsampling error?
- During the same year, another pollster conducted a poll of 30,000 prospective voters. These researchers used a method they called
*quota sampling*to obtain survey answers from specific subsets of the population. Quota sampling is an example of which sampling method described in this module?

Crime-related and demographic statistics for 47 US states in 1960 were collected from government agencies, including the FBI's *Uniform Crime Report*. One analysis of this data found a strong connection between education and crime indicating that higher levels of education in a community correspond to higher crime rates.

Which of the potential problems with samples discussed in Data, Sampling, and Variation in Data and Sampling could explain this connection?

A website that allows anyone to create and respond to polls had a question posted on April 15 which asked:

“Do you feel happy paying your taxes when members of the Obama administration are allowed to ignore their tax liabilities?”^{1}

As of April 25, 11 people responded to this question. Each participant answered “NO!”

Which of the potential problems with samples discussed in this module could explain this connection?

A scholarly article about response rates begins with the following quote:

“Declining contact and cooperation rates in random digit dial (RDD) national telephone surveys raise serious concerns about the validity of estimates drawn from such research.”^{2}

The Pew Research Center for People and the Press admits

“The percentage of people we interview—out of all we try to interview—has been declining over the past decade or more.”^{3}

- What are some reasons for the decline in response rate over the past decade?
- Explain why researchers are concerned with the impact of the declining response rate on public opinion polls.

### 1.3 Frequency, Frequency Tables, and Levels of Measurement

Fifty part-time students were asked how many courses they were taking this term. The (incomplete) results are shown below.

# of Courses | Frequency | Relative Frequency | Cumulative Relative Frequency |
---|---|---|---|

1 | 30 | .6 | |

2 | 15 | ||

3 |

- Fill in the blanks in Table 1.37.
- What percent of students take exactly two courses?
- What percent of students take one or two courses?

Sixty adults with gum disease were asked the number of times per week they used to floss before their diagnosis. The (incomplete) results are shown in Table 1.38.

# Flossing per Week | Frequency | Relative Frequency | Cumulative Relative Frequency |
---|---|---|---|

0 | 27 | .4500 | |

1 | 18 | ||

3 | .9333 | ||

6 | 3 | .0500 | |

7 | 1 | .0167 |

- Fill in the blanks in Table 1.38.
- What percent of adults flossed six times per week?
- What percent flossed at most three times per week?

Nineteen immigrants to the United States were asked how many years, to the nearest year, they have lived in the United States.

The data are as follows:

2, 5, 7, 2, 2, 10, 20, 15, 0, 7, 0, 20, 5, 12, 15, 12, 4, 5, 10

Table 1.39 was produced.

Data | Frequency | Relative Frequency | Cumulative Relative Frequency |
---|---|---|---|

0 | 2 | $\frac{2}{19}$ | .1053 |

2 | 3 | $\frac{3}{19}$ | .2632 |

4 | 1 | $\frac{1}{19}$ | .3158 |

5 | 3 | $\frac{3}{19}$ | .4737 |

7 | 2 | $\frac{2}{19}$ | .5789 |

10 | 2 | $\frac{2}{19}$ | .6842 |

12 | 2 | $\frac{2}{19}$ | .7895 |

15 | 1 | $\frac{1}{19}$ | .8421 |

20 | 1 | $\frac{1}{19}$ | 1.0000 |

- Fix the errors in Table 1.39. Also, explain how someone might have arrived at the incorrect number(s).
- Explain what is wrong with this statement: “47 percent of the people surveyed have lived in the United States for 5 years.”
- Fix the statement in
**b**to make it correct. - What fraction of the people surveyed have lived in the United States five or seven years?
- What fraction of the people surveyed have lived in the United States at most 12 years?
- What fraction of the people surveyed have lived in the United States fewer than 12 years?
- What fraction of the people surveyed have lived in the United States from five to 20 years, inclusive?

How much time does it take to travel to work? Table 1.40 shows the mean commute time by state for workers at least 16 years old who are not working at home. Find the mean travel time, and round off the answer properly.

24.0 | 24.3 | 25.9 | 18.9 | 27.5 | 17.9 | 21.8 | 20.9 | 16.7 | 27.3 |

18.2 | 24.7 | 20.0 | 22.6 | 23.9 | 18.0 | 31.4 | 22.3 | 24.0 | 25.5 |

24.7 | 24.6 | 28.1 | 24.9 | 22.6 | 23.6 | 23.4 | 25.7 | 24.8 | 25.5 |

21.2 | 25.7 | 23.1 | 23.0 | 23.9 | 26.0 | 16.3 | 23.1 | 21.4 | 21.5 |

27.0 | 27.0 | 18.6 | 31.7 | 23.3 | 30.1 | 22.9 | 23.3 | 21.7 | 18.6 |

A business magazine published data on the best small firms in 2012. These were firms which had been publicly traded for at least a year, have a stock price of at least $5 per share, and have reported annual revenue between $5 million and $1 billion. Table 1.41 shows the ages of the chief executive officers for the first 60 ranked firms.

Age | Frequency | Relative Frequency | Cumulative Relative Frequency |
---|---|---|---|

40–44 | 3 | ||

45–49 | 11 | ||

50–54 | 13 | ||

55–59 | 16 | ||

60–64 | 10 | ||

65–69 | 6 | ||

70–74 | 1 |

- What is the frequency for CEO ages between 54 and 65?
- What percentage of CEOs are 65 years or older?
- What is the relative frequency of ages under 50?
- What is the cumulative relative frequency for CEOs younger than 55?
- Which graph shows the relative frequency and which shows the cumulative relative frequency?

*Use the following information to answer the next two exercises:* Table 1.42 contains data on hurricanes that have made direct hits on the United States. Between 1851-2004. A hurricane is given a strength category rating based on the minimum wind speed generated by the storm.

Category | Number of Direct Hits | Relative Frequency | Cumulative Frequency |
---|---|---|---|

Total = 273 | |||

1 | 109 | .3993 | .3993 |

2 | 72 | .2637 | .6630 |

3 | 71 | .2601 | |

4 | 18 | .9890 | |

5 | 3 | .0110 | 1.0000 |

What is the relative frequency of direct hits that were category 4 hurricanes?

- .0768
- .0659
- .2601
- not enough information to calculate

What is the relative frequency of direct hits that were AT MOST a category 3 storm?

- .3480
- .9231
- .2601
- .3370

### 1.4 Experimental Design and Ethics

How does sleep deprivation affect your ability to drive? A recent study measured the effects on 19 professional drivers. Each driver participated in two experimental sessions: one after normal sleep and one after 27 hours of total sleep deprivation. The treatments were assigned in random order. In each session, performance was measured on a variety of tasks including a driving simulation.

Use key terms from this module to describe the design of this experiment.

An advertisement for Acme Investments displays the two graphs in Figure 1.14 to show the value of Acme’s product in comparison with the Other Guy’s product. Describe the potentially misleading visual effect of these comparison graphs. How can this be corrected?

The graph in Figure 1.15 shows the number of complaints for six different airlines as reported to the U.S. Department of Transportation in February 2013. Alaska, Pinnacle, and Airtran Airlines have far fewer complaints reported than American, Delta, and United. Can we conclude that American, Delta, and United are the worst airline carriers since they have the most complaints?

An epidemiologist is studying the spread of the common cold among college students. He is interested in how the temperature of the dorm room correlates with the incidence of new infections. How can he design an observational study to answer this question? If he chooses to use surveys in his measurements, what type of questions should he include in the survey?