Lecture 16 - Measuring disease occurrence Flashcards
Prevalence
The proportion of a population who have the disease at a point in time
- Burden of disease
- Resource allocation
Prevalence calculation:
Number of people with disease at given point in time / total number of people in the population at that point in time
- Disease / total population
Reporting prevalence
MOPTV
- Measure of occurrence
- Exposure or outcome
- Population
- Time point
- Value
Prevalence - limitations
- Difficult to assess the development of disease
- Is influenced by the duration of disease
Incidence
The occurrence of new cases of an outcome in a population during a specific period of follow up.
IP or IR
Incidence proportion
The proportion of an outcome free population that develops the outcome of interest in a specified time period
IP - calculation
Number of people who develop the disease in a specified period / number of people at risk of developing the disease at the start of the period.
- New Developed disease / population at risk
Limitation Incidence proportion:
- Assumes a closed population (no coming or going)
- Highly dependent on time period
Incidence rate
The rate at which new cases of the outcome of interest occur in a population
IR: Calculation
Number of people who develop the disease in a specific period / Number of person-years at risk of developing the disease
Why might someone stop being at risk
- They become a case
- They are lost to follow up
- Follow up time ends
IR: reporting
MOPV
- Measure of occurence
- Outcome
- Population
- Value
e.g. 50 per 100 person -year
IR limitations
- Person time not available
- Complex calculate
Prevalence, incidence and duration
P ~ I x D
- Changes to incidence and duration can affect disease prevalence
Age standardise the population:
- Techniques within allows populations to be compared when the age profiles of the populations are different
