chapter 9

Question 1

What is an observational study?

Answer 1

observes individuals and measures variables of interest but does not attempt to influence the responses. The purpose of an observational study is to describe some group or situation.

Question 2

What is an experiment?

Answer 2

deliberately imposes some treatment on individuals to observe their responses. The purpose of an experiment is to study whether the treatment causes a change in the response.

Question 3

What does it mean when two variables are confounded?

Answer 3

when their effects on a response variable cannot be distinguished from each other

Question 4

Define subjects

Answer 4

individuals studied in an experiment

Question 5

Define factors

Answer 5

explanatory variables in an experiment

Question 6

What is a control group?

Answer 6

receives either a standard treatment (which may be no treatment at all) or, in some cases, a sham treatment, and provides a basis for comparison with the other treatment groups

Question 7

What is a randomized comparative experiment?

Answer 7

An experiment that uses both comparison of two or more treatments and random assignment of subjects to treatments

Question 8

What happens in a completely randomized experimental design?

Answer 8

all the subjects are allocated at random among all the treatments

Question 9

What are the principles of experimental design?

Answer 9

control
randomization
replication

Question 10

What is a control?

Answer 10

restrict the effects of lurking variables on the response, most simply by comparing two or more treatments

Question 11

How is randomization used for experimental design?

Answer 11

use chance to assign subjects to treatments

Question 12

How is replication used for experimental design?

Answer 12

use enough subjects in each group to reduce chance variation in the results

Question 13

What does it mean to be statistically significant?

Answer 13

An observed effect so large that it would rarely occur by chance

Question 14

What is a placebo?

Answer 14

dummy treatment that is as similar to the treatment as possible but contains no active ingredient

Question 15

What are double blind experiments?

Answer 15

neither the subjects nor the people who interact with them know which treatment each subject is receiving

Question 16

Explain matched pairs design

Answer 16

Design of an experiment that compares two treatments. Each subject receives both treatments in random order, or the subjects are matched in pairs that are similar in some way that is expected to affect the response, and one subject in each pair receives each treatment

Question 17

What is a block?

Answer 17

a group of individuals that are known before an experiment to be similar in some way that is expected to affect the response to the treatments

Question 18

What is a block design?

Answer 18

the random assignment of individuals to treatments is carried out separately within each block

Question 19

Does peer victimization during adolescence have an impact on depression in early adulthood? A study in the United Kingdom examined data on 3898 participants for which the researchers had information on both victimization by peers at age 13 and the presence of depression at age 18. The study found more than a two-fold increase in the odds of depression between children who were not victimized and those who were frequently victimized.21 This is an example of

a. an observational study.
b. a randomized comparative experiment.
c. a block design, with level of victimization as the blocks.

Answer 19

a

Question 20

Migraine is a prevalent disease characterized by headaches that are often severe and throbbing and accompanied by associated symptoms, such as nausea, vomiting, vertigo, and cognitive dysfunction. A drug, fremanezumab, may be an effective preventive treatment for migraine. To investigate this, researchers give 20 migraine sufferers fremanezumab and observe whether the number of migraine days in a 12-week period is reduced. This is

a. an observational study.
b. an uncontrolled experiment.
c. a randomized comparative experiment.

Answer 20

b

Question 21

Does exposure to aircraft noise increase the risk of hospitalization for cardiovascular disease in older people
(
≥
 
65
 
years
)
residing near airports? Selecting a random sample of approximately 650,000 Medicare claims, it was found that about 75,000 people had zip codes near airports, and the remaining 575,000 did not. The proportions of hospital admissions related to cardiovascular disease were computed for those with zip codes near airports and those who did not have zip codes near airports. A larger proportion of admissions for cardiovascular disease was found for older people living in zip codes near airports. Which of the following statements is correct?

a. Since this is an observational study, living in a zip code near an airport may or may not be causing the increase in the proportions of admissions for cardiovascular disease.
b. Because of the large sample sizes from each group, we can claim that living in a zip code near an airport is causing the increase in the proportion of admissions for cardiovascular disease.
c. Because this is an experiment, although not a randomized experiment, we can still conclude that living in a zip code near an airport is causing the increase in the proportions of admissions for cardiovascular disease.

Answer 21

a

Question 22

To decide which community in each pair in the previous question should get the advertising campaign, it is best to
a. toss a coin
b. choose the community that will help pay for the campaign.
c. choose the community with a mayor who will participate.

Answer 22

a