Measuring Disease in Populations

Question 1

What is prevalence?

Answer 1

A measure of the number of existing cases on a specific date. It is expressed as a proportion of the population

Question 2

Define incidence

Answer 2

A measure of the population’s average risk of a disease

Question 3

Why is incidence not a valid way to measure risk of a disease to an individual?

Answer 3

There are variations in risk of disease between groups of people. Not all people have the same ‘proneness’ or ‘risk’ of getting a disease. This is called systematic variation

Question 4

How can systematic variation be helpful to statisticians?

Answer 4

The different levels of risk between groups of people can give a clue to the cause of a disease

Question 5

How is the Incidence Rate Ratio (IRR) worked out?

Answer 5

Incidence Rate (exposed)
-------------------------------- = IRR
Incidence Rate (unexposed)

Question 6

What is implied if the incidence rate of a disease in an exposed group, is higher than in an unexposed group?

Answer 6

The exposure is causing/aiding a disease

Question 7

How is a Mortality Rate Ratio (MRR) worked out?

Answer 7

Rate (old drug)

Question 8

What is implied if the MRR equals 1/2?

Answer 8

The new treatment HALVES the risk of deaths
OR
A patient is TWICE AS LIKELY to die on the old treatment

Question 9

List 2 determinants of health that cannot be altered

Answer 9

Age

Sex

Question 10

What is a confounding factor?

Answer 10

A factor that correlates to a higher incidence of disease but is not the causal factor. Eg. age

Question 11

How is the incidence rate of a disease worked out?

Answer 11

New events
—————————– = events per person per year
Population x time (years)