POPH192- Lecture 16 Flashcards
what do measures of occurence describe?
describes how often a disease pccurs in a population
what are the 3 measures of occurence?
- prevalence
- incidence proportion
- incidence rate
what is prevalence?
the proportion of a defined population who have a disease/outcome at a given point in time
what is the equation for prevalence?
prevalence = people with disease at point in time / total population at point in time
what is prevelance used to tell us?
to tell us how much disease/outcome is in a population and to help with resource allocation
what is the generic interpretation for prevalence?
the prevalence of outcome** in **population** at **timepoint** was **XX.X%
what are the limitations of prevalence?
- difficult to assess how disease/outcome developed
- influenced by duration of disease (diseases with longer duration have larger prevalence by default)
what is incidence?
the occurence of new cases of an outcome in a population during a specific period of follow up
what are the 2 types of incidence?
- incidence proportion
- incidence rate
what is the incidence proportion equation?
IP = number of people who develop disease / number of people at risk at start of follow up period
what is the incidence rate equation?
IR = number of people who develop disease / number of person years at risk
which equation should you use if you are given number of person years at risk
use incident rate equation
which equation should you use if you are given number of people at risk at start of follow up period?
incidence proportion equation
what is the interpretation of incidence proportion?
the incidence proportion of outcome in population over time period was XX.X%
what is the interpretation of incident rate?
the incidence rate of outcome in population was XX per X person years
what are some important things to remember for incidence rate? (4)
- always convert to years
- x100 to convert answer to ‘per 100 person years’
- sometimes you may need to interpret person years at risk from a graph/table
- need to add up person years at risk of all participants in the figure
when is a person so longer at risk?
when a participant drops out, dies, or develops the disease they are no longer at risk.
- only include ‘person years at risk’ in calculation
e. g. a person dropped out after 8 years of a study, so they contributed 8 person years at risk
what is the relationship between prevalence and incidence?
Prevalence is proportinal to incidence and duration
P ~ I x D
**do not use as an actual equation**
why is age standardisation necessary?
populations are not all the same.
- to compare rates of disease, we need to standardise populations
what is age standardisation?
a technique which allows populations to be compared when the age profiles of populations are different
what are the 2 criteria for age standardisation?
1) the age structures of populations differ
2) the disease risk vary by age
