Epidemiology

Question 1

Define epidemiology.

Answer 1

The study of the frequency, distribution and determinants of diseases and health related states in populations in order to prevent and control disease

Question 2

Define incidence.

Answer 2

Number of new cases in a specified time interval

Question 3

Define prevalence.

Answer 3

Number of existing cases at a specified point in time

Question 4

What is Person-Time and when is it used?

Answer 4

Person-time = measure of time at risk
Used to calculate incidence rate

Eg
Incidence rate = No of persons who have become cases in a given time period
Total person-time at risk during that period

= 3/32
= 0.094 per person-year
= 9.4 per 100 person-years

Question 5

Define public health.

Answer 5

The science and art of preventing disease, prolonging life and promoting health through organised efforts of society

Question 6

Define absolute risk.

Answer 6

Measurement of likelihood a certain event would happen

*has units

Question 7

Define relative risk.

Answer 7

Ratio of risk in exposed group to risk in not exposed group
*no units

RR>1 increased risk
RR=1 risk same whether or not exposed
RR<1 reduced risk

Question 8

Define attributable risk.

Answer 8

Rate of disease that can be attributed to exposure

Incidence in exposed minus unexposed

Question 9

From the following made up information, calculate attributable risk and relative risk:

Answer 9

Incidence of Disease A in smokers, 1/1000 person-years Incidence of Disease A in non-smokers, 0.05/1000 person-years

Attributable risk = 0.95/1000 person-years (i.e. difference)
Relative risk = 20 (i.e. ratio, no units)

Incidence of Disease B in smokers, 8/1000 person-years Incidence of Disease B in non-smokers, 4/1000 person-years

Attributable risk = 4/1000 person-years
Relative risk = 2

Question 10

Define Numbers Needed to Treat (NNT).

Answer 10

Numberof patientsyou need to treatto prevent one additional bad outcome
Formula = 1/absolute risk increase

Question 11

Define bias.

Answer 11

Systematic deviation from the true estimation of the association between exposure and outcome

Question 12

What are the 2 types of bias?

Answer 12

1. Selection Bias
   A systematic error in:
   the selection of study participants
   the allocation of participants to different study groups
2. Information (measurement) bias
   A systematic error in the measurement or classification of:
   exposure
   outcome

Sources of information bias:
observer (e.g. observer bias)
participant (e.g. recall bias)
instrument (e.g. wrongly calibrated instrument)

Question 13

Define confounding.

Answer 13

Situation where a factor is associated with the exposure of interest and independently influences the outcome (but does not lie on the causal pathway)

Question 14

If association not causal (non-causal associations), how could it be explained?

Answer 14

Bias
Chance
Confounding
Reverse causality

Question 15

What are the “Criteria” for causality (or factors to consider when assessing causality) based on the Bradford Hill Criteria?

Answer 15

Bradford Hill Criteria (Std crab)

1. Strength of association
   the magnitude of the relative risk
2. Dose-response
   the higher the exposure, the higher the risk of disease
3. Consistency
   similar results from different researchers using various study designs
4. Temporality
   does exposure precede the outcome?
5. Reversibility (experiment)
   removal of exposure reduces risk of disease
6. Biological plausibility
   biological mechanisms explaining the link

Question 16

Absolute risk difference/risk reduction/ risk excess

Answer 16

Absolute risk difference is the absolute additional risk of an event following an exposure.
ARD = risk in an exposed group – risk in unexposed group