lecture 16 Flashcards
what are the three measures of occurrence
- prevalence
- incidence proportion
- incidence rate
what is prevalence
the proportion of a population who HAVE the disease at a point in time
why do we want to know the prevalence of a disease
- info on the burden of disease
- resource allocation
how do you calculate prevalence
number of people with the disease at a given point in time / total number of people in the population at that point in time
how do you report prevalence
- the measure of occurrence
- exposure or outcome
- population
- time point
- value
what are the limitations to prevalence
- difficult to assess the development of disease
- is influence by the duration of the disease
if nothing else happens but the disease has a longer duration then what will happen to prevalence
the disease will be more prevalent
what is incidence
the occurrence of new cases of an outcome in a population during a specific period of follow up
what is incidence proportion
the proportion of an outcome free population that develops the outcome of interest in a specified time period
what is the calculation of incidence proportion
number of people who develop the disease in specified period / number of people at risk of developing the disease the disease at the start of the period
why might people not be considered ‘at risk’ at the start of a study
- they already have the condition
- the condition is something that they can not develop
how do you report incidence proportion
- measure of occurrence
- outcome
- population
- time period
- value
example of reporting prevalence on asthma
the prevalence of asthma in POPH192 class on August 16th 2023 was 10%
example of reporting incidence proportion on low back pain in nurses
the incidence proportion of low back pain in nurses in 12 months was 35%
what are the limitations of incidence proportion
- assumes a ‘closed’ population (does not account for people coming or going)
- highly dependent on the time period (longer time period = higher incidence proportion
what is the incidence rate
the rate at which new cases of the outcome of interest occur in a population
how to calculate incidence rate
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
how do you report incidence rate
- measure of occurrence
- outcome
- population
- value
example of reporting incidence rate on glandular fever
the incidence rate of glandular fever in the class was 50 per 100 person - years
what are the limitations of incidence rate
- person time not available
- complex to calculate
what is prevalence influenced by
both incidence and duration of the disease
what is age standardisation
removes the affect of the population having different age structures
