L16: Measuring Disease Occurrence

Question 1

What are the 4 stages/phases of the Public Health Model?

Answer 1

1) Defining and measuring the problem
2) Describing causes and consequences
3) Developing and evaluating interventions
4) Disseminating effective policy and practice

Question 2

What are the measures of occurrence?

Answer 2

Prevalence and Incidence (incidence proportion + incidence rate)

Question 3

This is the proportion of the population who have the disease at a point in time.

Answer 3

Prevalence

Question 4

What is the formula for prevalence?

Answer 4

Number of people with disease at a given point in time / Total number of people in the population at that point in time

Question 5

What are the 2 limitations of measuring prevalence?

Answer 5

• difficult to assess the development of disease (like when did it worsen or how did it happen)
• is influenced by the duration of the disease

Question 6

This measures the occurrence of new cases of an outcome in a population during a specific period of follow up.

Answer 6

Incidence

Question 7

This is the proportion of an outcome free population that develops the outcome of interest in a specific time period.

Answer 7

Incidence proportion

Question 8

What is the formula for incidence proportion?

Answer 8

Number of people who develop disease in a specific period / number of people at risk of developing the disease (usually those who don’t have it at the beginning of time period)

Question 9

Why might some people not be considered at risk at the start of a study?

Answer 9

They already have the condition.

The condition is something that cannot develop

Question 10

What are the 2 main limitations of incidence proportion?

Answer 10

• assumes a closed population (so does not account people coming and going)
• highly dependent on the time period (time-at-risk increases if time increases)

Question 11

This is the rate at which new cases of the outcome of interest occur in a population.

Answer 11

Incidence rate

Question 12

What is the formula for incidence rate?

Answer 12

Number of people who develop the disease in a specified period / number of person years at risk of developing the disease (total number of years a population is at risk)

Question 13

What are the 2 main limitations of incidence rate?

Answer 13

• person time not available (aka lost to follow up or no longer in the population)
• complex to calculate

Question 14

Prevalence approximates?

Answer 14

Incidence * duration

So changes to incidence and duration can affect disease prevalence

Question 15

When comparing populations, what 2 factors must be considered?

Answer 15

• age structure
• disease risk (does it vary by age?)

Question 16

Age standardisation occurs when what 2 factors are occurring?

Answer 16

When the age structure differs between population, and the disease risk varies by age (two variables for comparing populations)-