chapter 9 Flashcards
What is an observational study?
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.
What is an experiment?
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.
What does it mean when two variables are confounded?
when their effects on a response variable cannot be distinguished from each other
Define subjects
individuals studied in an experiment
Define factors
explanatory variables in an experiment
What is a control group?
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
What is a randomized comparative experiment?
An experiment that uses both comparison of two or more treatments and random assignment of subjects to treatments
What happens in a completely randomized experimental design?
all the subjects are allocated at random among all the treatments
What are the principles of experimental design?
control
randomization
replication
What is a control?
restrict the effects of lurking variables on the response, most simply by comparing two or more treatments
How is randomization used for experimental design?
use chance to assign subjects to treatments
How is replication used for experimental design?
use enough subjects in each group to reduce chance variation in the results
What does it mean to be statistically significant?
An observed effect so large that it would rarely occur by chance
What is a placebo?
dummy treatment that is as similar to the treatment as possible but contains no active ingredient
What are double blind experiments?
neither the subjects nor the people who interact with them know which treatment each subject is receiving
Explain matched pairs design
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
What is a block?
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
What is a block design?
the random assignment of individuals to treatments is carried out separately within each block
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.
a
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.
b
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.
a
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.
a
