41 - Observational Studies in CVD

Question 1

Cross-sectional studies

Answer 1

Sample of population, taken at one point in time (non-longitudinal)
Data taken from questionnaires, examinations, investigations, etc.

Question 2

Drawbacks of cross-sectional studies

Answer 2

Can’t really prove causation, as have no temporal component.

Question 3

Advantages of cross-sectional studies

Answer 3

Cheap, fast, relatively easy

Question 4

Case-control studies

Answer 4

Compare previous exposure status to risk factor between those known to have outcome (cases), and those without outcome (controls).
Non-longitudinal.

Question 5

Steps in case-control studies
1)
2)

Answer 5

1) Match cases and controls according to confounders (age, sex, etc).
2) Determine previous exposure among subjects

Question 6

Study type that is useful for studying rare outcomes

Answer 6

Case-control studies

Question 7

Why are case-control studies useful for studying rare outcomes?

Answer 7

Can select cases who have rare condition, instead of recruiting a large enough group of people to study so that one of them might develop condition

Question 8

Key output of case-control studies

Answer 8

Odds ratio (approximation of relative risk)

Question 9

Why is the key output of case-control studies an odds ratio, and not a relative risk?

Answer 9

Case-control studies are non-longitudinal. Relative risk requires longitudinal data to generate (relative risk is rate exposed/rate unexposed, and rate is the probability of disease occurring in an undiseased population over cumulative time of study).

Question 10

How is odds ratio calculated?

Answer 10

[odds of exposure to non-exposure among cases] ÷

[odds of exposure to non-exposure among controls]

Question 11

Cohort studies

Answer 11

Longitudinal studies.
Compare outcomes among subgroups (EG: disease in exposed/unexposed).
Collect incidence data

Question 12

Data output of cohort studies

Answer 12

Relative risk

Question 13

Difference between prospective and retrospective cohort study

Answer 13

Prospective is where subjects are recruited before outcome has occurred.
Retrospective is where subjects are recruited after outcome has occurred.

Question 14

Advantages of cohort studies

Answer 14

explicit (often-detailed) knowledge about temporal
relationship between exposure and outcome
• can include multiple exposures and outcomes
• research hypotheses can be addressed post hoc in
established cohorts

Question 15

Disadvantages of cohort studies

Answer 15

1) Hard to study rare outcomes

2) Difficult to carry out, expensive

Question 16

Study that gave data for interactions between CVD risk factors

Answer 16

Framingham study

Question 17

Bias

Answer 17

Unintentional error leading to systematic difference between or among groups

Question 18

Two main types of bias

Answer 18

Selection bias

Information bias

Question 19

Selection bias

Answer 19

Systematic difference in people selected for study (EG: type of people willing to enter study might be unrepresentative).

Question 20

Example of selection bias

Answer 20

Difference between subjects who stay in Framingham study, and those who drop out

Question 21

Ways to minimise selection bias
1)
2)
3)

Answer 21

1) Careful recruitment (cases and controls from the same place)
2) Maximise results.
3) Careful follow up

Question 22

Information bias

Answer 22

Systematic differences in way that data is gathered between or among groups.
Particularly arises when there is variability (subjectivity) in how data are collected.

Question 23

Example of information bias

Answer 23

Differential in how CVD was measured between males and females in Framingham study

Question 24

Universal confounders

Answer 24

Age, sex