Epidemiology - Key Concepts

Question 1

Define Epidemiology.

Answer 1

The study of the distribution and determinants of health-related states or events in specified population and the application of this study to control of health problems

Question 2

What are the three components of the epidemiological triad?

Answer 2

Time
Place
Person

Question 3

List some factors that are included under the heading of ‘Time”.

Answer 3

Long-term (secular)
Epidemic (temporary increase)
Periodical (cyclical)
Seasonal

Question 4

List some factors that are included under the heading of ‘Place’.

Answer 4

Geographical
Local
Workplace
Community
Home
Social gatherings

Question 5

List some intrinsic & extrinsic factors that are included under the heading of ‘Person’.

Answer 5

Intrinsic:

• genetics
• age
• sex
• marital status
• ethnic group

Extrinsic:

• lifestyle
• behaviour
• occupation
• migration
• socio-economic

Question 6

List the 7 stages of the continuum of health.

Answer 6

Healthy
Disease onset
Symptoms
Seek care
Diagnosis
Treatment
Outcome

Question 7

What are the 4 elements of the epidemiologists bathtub?

Answer 7

Incidence
Recovery
Prevalence
Death/Mortality

Question 8

Define incidence.

Answer 8

The rate at which new cases occur in a population during a specific period

Question 9

Define prevalence.

Answer 9

The number of existing cases in a population at a point in time

Question 10

What can affect the prevalence?

Answer 10

Recovery & death

Question 11

How is the incidence rate calculated?

Answer 11

Number of new people with outcome over a time period (either recovery or death) x100000
____________________
Total number of people in the group at risk during that time period

Question 12

How is the prevalence rate calculated?

Answer 12

Number of people with outcome at a point in time x100
____________________
Total number of people in the group

Question 13

What is the difference between point prevalence and period prevalence?

Answer 13

Point prevalence: at one point in time

Period prevalence: over a time period

Question 14

Study designs can be categorised. List the studies that fall under the heading, ‘Observational’.

Answer 14

Ecological
Case series
Cros-sectional
Cohort
Case-control

Question 15

Study designs can be categorised. List the studies that fall under the heading, ‘Experimental’.

Answer 15

Quasi-experiment

RCT (randomised controlled trial)

Question 16

What is meant by ecological fallacy?

Answer 16

Individual variation in a population

Question 17

How is an ecological study similar to a case-series?

Answer 17

The only difference is that a case-series is individually focused, whereas an ecological study is focused on a population; unit of study is a population as opposed to an individual

Question 18

Give a good example of an ecological study.

Answer 18

John Snow and his discovery of the outbreak of cholera source in London - Broad Street Pump

Question 19

Briefly summarise what a case control study is.

Answer 19

Cases have the disease/condition
Controls don’t have the disease/problem
These are the OUTCOMES
Therefore, you need to look BACKWARDS in order to ascertain what proportion of cases and controls had undergone EXPOSURE

Question 20

How is a cohort study similar to a case control study?

Answer 20

A cohort study is also retrospective - look backwards to explore exposure

Question 21

Explain how a cohort study is conducted.

Answer 21

Gather a population free of disease
Expose one group to the disease, leave the other group unexposed
Assess outcome of each group - where is greatest incidence of disease

Question 22

What is a case series?

Answer 22

A series of cases with the same disease (often consecutive)

Question 23

List the 3 steps of conducting a cross-sectional study

Answer 23

1. Sample a population
2. Estimate the proportion - different exposures, signs, symptoms & outcomes
3. Use data for reinforcement and to describe prevalence/explore associations

Question 24

How is a RCT conducted?

Answer 24

Population chosen at RANDOM
One randomly selected group - intervention
The other randomly selected group - control