Chapter 8: Cohort Studies Flashcards
Explain the design of a cohort study
In a cohort study, the investigator selects 2 or more groups of exposed and non-exposed individuals and follows them for an extended period of time (time may vary but can be years later) to compare the rate of incidence or deaths from a disease between the groups.
True or False: In a positive association we would see all of the groups develop the disease and thus an increase in the incidence would occur.
False. In a positive association we would see an increase portion of the exposure group develop the disease and thus an increase in the incidence would occur in the exposed group.
True or False: Thus the purpose of a cohort study is because we are identifying new induce rates cases of disease as they occur, we determine whether or not a temporal relationship exists where the disease develops after exposure.
True
What is the key difference between a cohort study and a Randomized trial?
The presence or absence of randomization
Define a retrospective cohort study?
Retrospective Cohort Study uses the same design as a the cohort but in addition to the use of historical data gathered.
What potential Biases can occur in a cohort study?
1) Bias in the assessment of the outcome due to previous knowledge of the exposure.
2) Information Bias in regard to the amount of information or quality of information gathered from the exposed and non-exposed groups.
3) Bias due to non-response and loss to follow-up
4) Analytic Bias epidemiologist may introduce their own bias.
When is a cohort study warranted?
When good evidence suggest a possible association of disease with a certain exposure obtained through clinical observation, case-control, or other forms of scientific field study.
What are other names for a prospective cohort study?
Concurrent cohort or longitudinal study
What type of diseases are particularly appealing to use the a cohort study design?
The study of childhood diseases and health
In cohort studies of the role of a suspected factor in the etiology of a disease, it is essential that:
The exposed and unexposed groups under study be as similar as possible with regard to possible confounding factors
Which of the following is not an advantage of a prospective cohort study?
a. It usually costs less than a case control study
b. Precise measurement of exposure is possible
c. Incidence rates can be calculated
d. Recall bias is minimized compared with case-control study
e. Many disease outcomes can be studied simultaneously
It usually costs less than a case control study
Retrospective cohort studies are characterized by all of the following except:
a. the study groups are exposed and unexposed
b. incidence rates may be computed
c. the required sample size is smaller than that needed for a prospective cohort study
d. the required sample size is similar to that needed for a prospective cohort study
e. they are useful for rare exposures
c. the required sample size is smaller than that needed for a prospective cohort study
A major problem resulting from the lack of randomization in a cohort study is:
a. the possibility that a factor that led to the exposure, rather than the exposure itself, might have caused the disease
b. the possibility that a greater proportion of people in the study may have been exposed
c. the possibility that smaller proportion of people in the study may been exposed
d. that, without randomization, the study may take longer to carry out
e. planned crossover is more likely
a. the possibility that a factor that led to the exposure, rather than the exposure itself, might have caused the disease
In a cohort study, the advantage of starting by selecting a defined population for study before any of its members become exposed, rather than starting by selecting exposed and unexposed individuals, is that:
A number of exposures can be studied simultaneously
What is the purpose of randomization?
Prevent any potential biases from investigator
What are the advantages of cohort studies?
- Lack of bias in determining exposure
- Yields incidence rate and relative risk
- Efficient for studying rare exposures
- Can yield association w/additional disease outcomes as well as targeted outcome
What are the disadvantages of cohort studies?
- Possible bias in ascertainment of disease
- Large number of subjects required
- Long follow-up period
- Problem of attrition
- Costly
- Criteria/methods change overtime
What is the weakest study design?
Cross-sectional
What is ecological fallacy?
Working with data that is at the group rather than the individual level of analysis
Odds ratios are used in what study design?
Case control studies
Relative risk is used in what study design?
Cohort studies
What are the advantages of case control studies?
- Relatively inexpensive
- Smaller number of subjects
- Relatively quick results
- Suitable for rare diseases
What are the disadvantages of case control studies?
- Incomplete exposure info
- Biased recall
- Yields only estimate or relative risk
- Problems selecting control group and matching variables
