EPIDEMIOLOGY

Question 1

Define Outcome, Exposure, Risk factor

Answer 1

• Outcome –The disease or occurrence of event being studied (e.g. T2D or a CVD event)
• Exposure - Any characteristic that may be related to a study outcome
• Risk Factor - Any characteristic associated with a higher likelihood of developing an
outcome of interest. These can be grouped into modifiable or non-modifiable risk
factors

Question 2

Overview of study designs in Epidemiology

Answer 2

Observational
Study:

Cohort Study
Starts with the outcome of
interest and looks back in time at exposures

Case-control Study
Starts with the exposures and looks forward in time at who develops the outcome of interest

Cross-sectional Study
Looks at exposures and the
outcome of interest at same time

Question 3

Difference between observation studies and experimental/intervention studies

Answer 3

Did the
researcher assign
the exposure?

No = O
Yes = E/I

Question 4

Prospective Cohort

Answer 4

• Population & risk factor defined
• Participants classified as exposed or unexposed to chosen risk factor
• follows participant over time
• During baseline and follow up, confounding variables taken
• End = outcome of interest assessed

Question 5

Retrospective Cohort

Answer 5

• exposure data taken from past record instead of recruiting people in present day
• Outcomes have already occurred in the past
• historical records used to classify individuals as exposed or unexposed to risk factor at chosen baseline of time
• Other available risk factors recorded at baseline
• past record for info on risk factors and outcome throughout follow-up

Question 6

What is a confounder?

Answer 6

A confounder is a variable which is:

• Associated with the exposure of interest
• Independently associated with the risk of developing the outcome

Confounding can:
• Lead to an under- or over-estimation of a real association between Exposure and Outcome
• Produce a spurious positive or negative association between Exposure and Outcome

Question 7

Risk ratio or relative risk (RR)

Answer 7

𝑅𝑅 = 𝑅𝑖𝑠𝑘𝑜𝑓𝑑𝑖𝑠𝑒𝑎𝑠𝑒𝑖𝑛𝑒𝑥𝑝𝑜𝑠𝑒𝑑𝑔𝑟𝑜u𝑝/𝑅𝑖𝑠𝑘𝑜𝑓𝑑𝑖𝑠𝑒𝑎𝑠𝑒𝑖𝑛𝑈𝑁𝑒𝑥𝑝𝑜𝑠𝑒𝑑𝑔

RR=1
RR>1
RR<1

• Caution! Relative Risk tells you nothing about absolute risk

Question 8

difference between incidence and Prevalence

Answer 8

Incidence =
Number of new cases of disease
which develop in a population
over a period of time

Prevalence =
Number of existing cases of a
disease in a population

Question 9

Advantages of Cohort studies

Answer 9

-Exposure is measured before disease,
reducing potential for bias, and
allowing causality to be assumed

-Multiple outcomes (diseases) can be
studied for any one exposure

-Incidence of disease can be
measured in the exposed and
unexposed groups

Question 10

Disdvantages of Cohort studies

Answer 10

-Slow, expensive, administratively
difficult & complex

-Needs large numbers –especially
when interested in a rare disease

-Collection of data may alter
behaviour

-Losses to follow-up

Question 11

Advantages of Case control studies

Answer 11

• Good for rare outcomes
• Quick & easy to carry out
• Relatively low cost
• Can investigate multiple exposures/
  risk factors

Question 12

Disadvantages of Case control studies

Answer 12

• Prone to bias, especially recall bias
• Selection of controls can be difficult
• Can only investigate one disease
• Cannot measure incidence