Chapter 7: Observational Studies

Question 1

A case-control study is characterized by all of the following except:

a. It is relatively inexpensive compared with most other epidemiologic study designs
b. Patients with the disease (cases) are compared with persons without the disease (controls)
c. Incidence rates may be computed directly
d. Assessment of past exposure may be biased
e. Definition of cases may be difficult

Answer 1

C: Incidence rates may be computed directly

Question 2

Residents of three villages with three different types of water supply were asked to participate in a survey to identify cholera carriers. Because several cholera deaths had occurred recently, virtually everyone present at the time underwent examination. The proportion of residents in each village who were carriers was computed and compared. What is the proper classification for this study?

Answer 2

A: Cross-Sectional

Question 3

Obtaining histories and other information from a group of known cases and from a comparison group to determine the relative frequency of a characteristic or exposure under study is an example of what study design?

Answer 3

Case-Control Study

Question 4

In a study begun in 1965, a group of 3,000 adults in Baltimore were asked about alcohol consumption. The occurrence of cases of cancer between 1981 and 1995 was studied in this group. This is an example of:

Answer 4

Prospective Cohort Study

Question 5

In a small pilot study, 12 women with endometrial cancer (cancer of the uterus) and 12 women with no apparent disease were contacted and asked whether they had ever used estrogen. Each women with cancer was matched by age, race, weight, and parity to a woman without disease? What kind of study design is this?

Answer 5

Case-Control Study

Question 6

In which of the following types of study designs does a subject serve as his own control?

a. Prospective
b. Restrospective
c. Case-cohort
d. Case-crossover study
e. Case-control study

Answer 6

Case-crossover study

Question 7

In a case-control study, when is the exposure determined?

Answer 7

Past (retrospectively)

Question 8

In a case-control study, when are cases and controls selected?

Answer 8

At the time of the study (present)

Question 9

In a prospective cohort study, when is the exposure determined?

Answer 9

At the start of the study (present)

Question 10

How do you calculate an odds ratio?

Answer 10

= ad/bc

Question 11

In case-control studies what is generally matched between cases and controls?

Answer 11

Age, sex, SES if possible

Question 12

What is the hallmark difference between a case-control study and a cohort study?

Answer 12

A case-control study begins with people with the disease (cases) and compares them to people withouth the disease (controls)

A cohort study starts with a group of exposed people and compares them to an unexposed group

Question 13

Why is it preferred to use incident cases over prevalent cases in case-control studies?

Answer 13

It is generally preferred to use incident cases of the disease because including prevalent cases maybe more indicative of survival with the disease compared to development (incidence)

Question 14

True or False: Comparison is an essential component of epidemiologic investigations and is well exemplified by the case-control study design.

Answer 14

True

Question 15

Explain the design of a Case-Control Study.

Answer 15

In order to examine a possible relation to an exposure of to a certain disease the design, we identify individuals with the disease (cases) and those without (controls). Where we determine what proportion of the two groups were exposed and non-exposed of past exposure. This can be done by interviewing, reviewing medical records, employee records, and the results of chemical or biological assays.

a- cases who were exposed
b- cases who were not exposed
c- controls who were exposed
d- controls who were not exposed

Question 16

How can case participant be selected for the case-control studies? And what factors do you have to keep in mind?

Answer 16

Patients may be obtained through a variety of sources such as a registry, a hospital, a physicians clinic and serve as a valuable source for such studies. Though it is important to keep in mind that the case-control criteria be carefully specified and the selection of individuals from a single hospital or source may be unique to that source (concern for generalizability?)

Question 17

What major concern can arise when conducting a case-control study?

Answer 17

A major concern when conducting a case-control study is the that cases and controls may differ in the characteristics or exposures other than the one that has been targeted for study.

Question 18

Describe individual matching?

Answer 18

Individual Matching- for each case that is selected for the study, a control is selected; who is similar to the cases in terms of specific variables of concern.

Question 19

Describe group matching (frequency matching)?

Answer 19

Group Matching (Frequency Matching)-consists of selecting the controls in such manner that the proportion of controls and cases with a certain characteristic is identical to each other