Measuring Disease Occurance

Question 1

Defining and measuring the problem

Answer 1

Concerned with describing who has a disease, what the disease is and when and where the disease is occurring
Interested in health status of population - pattern of disease in population, occurrence in different groups, trends over time

Question 2

What does prevalence mean and how do we calculate it?

Answer 2

Prevalence is the proportion of a population who have the disease at a point in time
Calculated: no. of people with disease at given point in time/total number of people in population at that point in time

Question 3

What are limitations of prevalence?

Answer 3

Limitations include difficulty in assessing the development of disease and it being influenced by the duration of the disease

Question 4

What is incidence of a disease?

Answer 4

Incidence is the occurrence of new cases of an outcome in a population during a specific period of follow up

Question 5

What is Incidence proportion?

Answer 5

Incidence proportion is the proportion of an outcome free population that develops the outcome of interest in a specified time period

Calculation: Number of people who develop disease/number of people at risk of developing disease at start of period

Question 6

What are limitations of Incidence proportion

Answer 6

Limitations include: assumes a closed population (not accounting for people coming or going), highly dependent on the time period (longer period = higher incidence proportion)

Question 7

What is Incidence rate

Answer 7

Incidence rate is the rate at which new cases of the outcome of interest occurs in a population
Calculation: number of people who develop disease in specified period/number of person years at risk of developing disease

Question 8

Why might someone stop being ‘at risk’?

Answer 8

Someone who become a case stop being at risk of it. If people stop taking part in the studying (lost of follow up) they stop being at risk. Follow up time ends - stop being at risk

Question 9

What are limitations of incidence rate?

Answer 9

Limitations of incidence rate include some people’s person-time not being available and it is complex to calculate

Question 10

What is age standardisation?

Answer 10

Age standardisation is where age structures differ and disease risk varies by age
Standardisation removes effect of different age group populations
Age structures must be different in populations and disease risk must vary by age before we age standardise a population