Week 6: Design 2

Question 1

1. What are cohort studies and how are they different from repeated cross-sectional studies?
2. in cohort studies, the _______ is determined before the _________ happens

Answer 1

1. cohort studies = group of individuals followed over time. They are different because the same individuals are followed up with NOT different ones like in repeated cross sectional
2. exposure before outcome

Question 2

What are prospective cohort studies? What are the benefits/drawbacks?

Answer 2

They follow the same patients FORWARD in time.
- More expensive, time consuming
- not efficient for diseases with long latent periods
- better exposure and confounder data
- less vulnerable to information bias

Question 3

what are retrospective cohort studies? what are the benefits and drawbacks?

Answer 3

they follow the same patients BACK in time. Some of the participants have already gotten the disease, so the purpose is to go back in time and find the exposures that led to the disease
- cheaper, faster, efficient with diseases with long latent periods
- exposure and confounder data may be inadequate
- more vulnerable to bias
- need an established recording system

Question 4

T/F: in a cohort study, a disadvantage is selection bias loss to follow up.

Answer 4

T

Question 5

1. What is a case control study?
2. do they look prospectively or retrospectively about exposures?

Answer 5

1. A study that compares patients who have a disease (cases) with patients who do not have the disease (controls).
2. retrospectively about past exposures

Question 6

What are controls?

Answer 6

Sample of the source pop that produced the cases

Question 7

What are the 2 criteria for selecting controls in a case-control study?

Answer 7

1. controls must come from the SAME SOURCE POP as the cases
2. controls must be SELECTED INDEPENDENTLY of EXPOSURE

Question 8

1. What is population based controls?
2. What are some sources for pop based controls
3. What are the drawbacks of this?

Answer 8

1. controls selected from a general population/well defined geographic area
2. random digit dialling, internet subscribers, residence lists
3. time consuming, hard to inspire participation, may not recall past exposures as well as cases

Question 9

1. What is nested controls?
2. What are some sources for pop based controls
3. What are the benefits and drawbacks of this?

Answer 9

1. controls selecting from an existing cohort group
2. already existing cohorts
3. benefits = controls are from a well defined source pop, already enrolled and willing participants
   drawbacks = restricted to only the existing cohort

Question 10

1. What is hospital or clinic based controls?
2. What are the benefits and drawbacks of this?

Answer 10

1. controls selected from patients at a hospital
2. A= easy to identify and access, less time and money, good recall, more willing
   D = not randomly selected

Question 11

T/F: case control studies are optimal for rare diseases

Answer 11

T

Question 12

Identify the correct measure of association for each type of study:
1. cross-sectional
2. case control
3. cohort (pro/retrospective)

Answer 12

1. PR (RR)
2. OR
3. IR (RR)

Question 13

1. What is the matching principle?
2. Explain individual vs frequency matching
3. what happens in case-control matching?

Answer 13

1. making groups as similar as possible so confounding doesn’t occur.
2. individual matching = performed participant by participant
   frequency matching = providing similar distributions of confounders in groups
3. after selection of the matching factor ex: gender. for each case, a control with the same characteristics will be selected