Study designs

Question 1

Three types of ecologic variables?

Answer 1

• Aggregate measures (means, proportions of individual characteristics)
• Environmental measures (geographic characteristics)
• Global measures (systemic characteristics)

Question 2

Synonym for ecological fallacy?

Answer 2

Aggregation bias

Question 3

2 times when ecological studies are a good choice?

Answer 3

1. When we intend to infer at the population level (e.g., for implications and interventions at population level)
2. When the variability of the exposure within the population is limited

Question 4

4 advantages of ecologic studies?

Answer 4

• Greater population coverage (so better generalizability)
• Some exposures better captured
• Greater exposure variation
• Cheap

Question 5

4 disadvantages of ecologic studies?

Answer 5

• Harder to control confounding
• Secondary data
• Temporal relationship difficult to define
• Ecological fallacy

Question 6

2 advantages and 1 disadvantage of prospective/concurrent cohort studies?

Answer 6

Advantages:

1. Measurement of all variables
2. Temporal ordering

Disadvantages:
1. Expensive, in money and time

Question 7

2 advantages and 1 disadvantage of retrospective/non-concurrent and mixed cohort studies?

Answer 7

Advantages:

1. Cheaper
2. Linking data registries

Disadvantages:
1. Data already collected, not necessarily of high quality or for research purposes

Question 8

4 assumptions of case-crossover studies?

Answer 8

1. The exposure varies over time
2. The exposure has a short induction time and a transient effect
3. No cumulative effect of exposure
4. Confounding factors do not vary over time

Question 9

Case-based case control study:

• Sampling method?
• Measure of association?

Answer 9

• At the end of the follow-up

- If rare disease, the OR estimates the risk ratio

Question 10

Nested case-control study:

• Sampling method?
• Measure of association?

Answer 10

• Concurrently (cumulative)

- Rate ratio (when matched on time analysis)

Question 11

Case-cohort study:

• Sampling method?
• Measure of association?

Answer 11

• Beginning of follow-up
• Risk ratio (if censoring unrelated to exposure)
• We can using this control group for multiple outcomes

Question 12

3 assumptions of survival analysis:

Answer 12

1. Censoring independent of survival
2. No secular trends
3. Uniform losses and events

Question 13

Prevalence odds formula?

Answer 13

Incidence Rate x 1/RR