Epidemiological Studies

Question 1

Objective: RCT

Answer 1

Investigating the effects of different interventions on dis-ease incidence in different groups of individuals. Usually used for clinical trials.

Question 2

Objective: Cohort Studies

Answer 2

Investigating the association between exposures eg: risk factors and dis-ease incidence.
Attempts to determine causes of dis-ease

Question 3

Objective: Cross Sectional Studies

Answer 3

To investigate the association between dis-ease prevalence and exposures eg: risk factors.
To measure prevalence in a population.

Question 4

Objective: Ecological Studies

Answer 4

To investigate associations between risk factors and dis-ease prevalence/incidence in different groups of populations.
i.e: Same as cohort studies, but instead populations are used instead of individuals.
Used to study dis-ease trends.

Question 5

Features: RCT

Answer 5

EG and CG assigned randomly.
Experimental-something is done to participants
Outcomes measured after a followup period.
Usually double-blinded to reduce effects such as reverse causality

Question 6

Features: Cohort Study

Answer 6

EG and CG assigned by measurement-observational.

Outcomes measured as the incidence of dis-ease during the followup period.

Question 7

Features: Cross-sectional study

Answer 7

EG and CG assigned by measurement-observational.

Participants assigned to EG and CG at the same time as measurement.

Question 8

Features: Ecological Study

Answer 8

Can be both experimental and observational.
Populations are assigned to EG and CG, instead of individuals.
Longitudinal and cross sectional.

Question 9

Advantages and Disadvantages: RCT

Answer 9

ADV: Randomisation of participants into EG or CG reduces confounding.
DIS: RCTs very costly so large RCTs are expensive. Most RCTs are too small so random error is too large.
Ethical problems prevent some investigations.
Logistics of maintaining exposure/control status is difficult- significant maintenance error.

Question 10

Advantages and Disadvantages: Cohort studies

Answer 10

ADV: Cheaper. Outcomes measured after exposure (prospective) measurement so there is no risk of reverse causality.
DIS: Significant confounding error.
Maintenance error as it is hard to enforce exposure/comparison status.

Question 11

Advantages and Disadvantages: Cross-sectional Study

Answer 11

ADV: Cheaper. Can be quickly completed as no follow up. Similarly NO MAINTENANCE ERROR.
DIS: Retrospective so uncertain time sequence. Potential reverse causality. Confounding error significant.

Question 12

Advantages and Disadvantages: Ecological Study

Answer 12

ADV: Cheaper and quicker than Cohort as it uses data that has already been collected by gov’t.
Useful when measuring exposures that are ubiquitous to some populations but not to others.
Useful for rare outcomes-representative sample so the occurrence is easily interpreted.
DIS: Confounding very common as data on confounding factors are usually absent.