measures of occurrence Flashcards
measures of occurrence
used to describe how often disease (or outcome) occurs in a population
three measures of occurrence
1) prevalence
2) incidence proportion
3) incidence rate
prevalence
- the proportion of a defined population who have a disease at a single point in time
prevalence equation
prevalence = people with disease @ point in time / total population @ point in time
what does prevalence tell us
tell us how much disease/outcome is in a population and to help with resource allocation
eg: if type 2 diabetes has the highest prevalence in Northland, NZ then we should allocate the highest amount of resources there
limitations of prevalence
- difficult to assess how the disease/outcome developed
- influenced by the duration of disease, diseases with a longer duration have a larger prevalence by default
incidence
- the occurrence of new cases of an outcome in a population during a specific period of follow up
two types of incidence
- incidence proportion
- incidence rate
incidence proportion
incidence proportion = no. of people with disease/ no. of people at risk at start of follow up period
incidence rate
incidence rate = no. of people who develop disease / no. of person yrs at risk
prevalence and incidence
- prevalence is proportional to incidence and duration
p ~ I x D - longer duration, higher prevalence (cases remain for longer in the prevalence pool)
- increase in incidence (new cases) higher prevalence (more cases entering the prevalence pool)
age standardisation
- populations are not all the same, to compare rates of disease we need to standardise the populations
- age standardisation is a technique which allows populations to be compared when the age profiles of the populations are different
criteria for age standardisation
1) the age structures of the population differ
2) the disease risk vary by age (eg: osteoporosis risk increases as people get older)
