Unit 3 AP Stats Review

When we take a census, we attempt to collect data from

• a stratified random sample

• every individual selected in an SRS

• every individual in the population

• a voluntary response sample

• a convenience sample

A study of treatments for angina (pain due to low blood supply to the heart) compared bypass surgery, angioplasty, and use of drugs. The study looked at the medical records of thousands of angina patients whose doctors had chosen one of these treatments. It found that the average survival time of patients given drugs was the highest. What do you conclude?

• This study proves that drugs prolong life and should be the treatment of choice.

• We can conclude that drugs prolong life because the study was a comparative experiment.

• We can’t conclude that drugs prolong life because the patients were volunteers.

• We can’t conclude that drugs prolong life because the groups might differ in ways besides the treatment.

• We can’t conclude that drugs prolong life because no placebo was used.

Tonya wanted to estimate the average amount of time that students at her school spend on Facebook each day. She gets an alphabetical roster of students in the school from the registrar’s office and numbers the students from 1 to 1137. Then Tonya uses a random number generator to pick 30 distinct labels from 1 to 1137. She surveys those 30 students about their Facebook use. Tonya’s sample is a simple random sample because

• it was selected using a chance process.

• it gave every individual the same chance to be selected.

• it gave every possible sample of size 30 an equal chance to be selected.

• it doesn’t involve strata or clusters.

• it is guaranteed to be representative of the population.

Consider an experiment to investigate the effectiveness of different insecticides in controlling pests and their impact on the productivity of tomato plants. What is the best reason for randomly assigning treatment levels (spraying or not spraying) to the experimental units (farms)?

• Random assignment eliminates the effects of other variables, like soil fertility.

• Random assignment eliminates chance variation in the responses.

• Random assignment allows researchers to generalize conclusions about the effectiveness of the insecticides to all farms.

• Random assignment will tend to average out all other uncontrolled factors such as soil fertility so that they are not confounded with the treatment effects.

• Random assignment helps avoid bias due to the placebo effect.

Researchers randomly selected 1700 people from Canada and rated the happiness of each person. Ten years later, the researchers followed up with each person and found that people who were initially rated as happy were less likely to have a heart problem. Which of the following is the most appropriate conclusion based on this study?

• Happiness causes better heart health for all people.

• Happiness causes better heart health for Canadians.

• Happiness causes better heart health for the 1700 people in the study.

• Happier people in Canada are less likely to have heart problems.

• Happier people in the study were less likely to have heart problems.

The sales force for a publishing company is constantly on the road trying to sell books. As a result, each salesperson accumulates many travel-related expenses that he or she charges to a company-issued credit card. To prevent fraud, management hires an outside company to audit a sample of these expenses. For each salesperson, the auditor prints out the credit card statements for the entire year, randomly chooses one of the first 20 expenses to examine, and then examines every 20th expense from that point on. Which type of sampling method is the auditor using for each salesperson?

• convenience sampling

• simple random sampling

• stratified random sampling

• cluster sampling

• systematic random sampling

Bias in a sampling method is

• any difference between the sample result and the truth about the population

• the difference between the sample result and the truth about the population due to using chance to select a sample

• any difference between the sample result and the truth about the population due to practical difficulties such as contacting the subjects selected

• any difference between the sample result and the truth about the population that tends to occur in the same direction whenever you use this sampling method

• racism or sexism on the part of those who take the sample

You wonder if TV ads are more effective when they are longer or repeated more often or both. So you design an experiment. You prepare 30-second and 60-second ads for a camera. Your subjects all watch the same TV program, but you assign them at random to four groups. One group sees the 30-second ad once during the program; another sees it three times; the third group sees the 60-second ad once; and the last group sees the60-second ad three times. You ask all subjects how likely they are to buy the camera.

Which of the following best describes the design of this experiment?

• This is a randomized block design, but not a matched pairs design.

• This is a matched pairs design.

• This is a completely randomized design with one explanatory variable (factor).

• This is a completely randomized design with two explanatory variables (factors).

• This is a completely randomized design with four explanatory variables (factors).

Can texting make you healthier? Researchers randomly assigned 700 Australian adults to either receive usual health care or usual heath care plus automated text messages with positive messages, such as “Walking is cheap. It can be done almost anywhere. All you need is comfortable shoes and clothing.” The group that received the text messages showed a statistically significant increase in physical activity “statistically significant” in this context?

• The results of this study are very important.

• The results of this study should be generalized to all people.

• The difference in physical activity for the two groups is greater than 0.

• The difference in physical activity for the two groups is very large.

• The difference in physical activity for the two groups is larger than the difference that could be expected to happen by chance alone.

You want to know the opinions of American high school teachers on the issue of establishing a national proficiency test as a prerequisite for graduation from high school. You obtain a list of all high school teachers belonging to the National Education Association (the country’s largest teachers’ union) and mail a survey to a random sample of 2500 teachers. In all, 1347 of the teachers return the survey. Of those who responded, 32% say that they favor some kind of national proficiency test. Which of the following statements about this situation is true?

• Since random sampling was used, we can feel confident that the percentage of all American high school teachers who would say they favor a national proficiency test is close to 32%.

• We cannot trust these results, because the survey was mailed. Only survey results from face-to-face interviews are considered valid.

• Because over half of those who were mailed the survey actually responded, we can feel pretty confident that the actual percent of all American high school teachers who would say they favor a national proficiency test is close to 32%

• The results of this survey may be affected by nonresponse bias.

• The results of this survey cannot be trusted due to voluntary response bias.