1.2 Basic Measurements Flashcards
Define Prevalence
The proportion of individuals in a population who have a disease or an attribute at a specified point in time.
Prevalence = No. with disease at a point in time/total no. in population
Can be reported as a proportion, percentage or per 100^n people.
Define: Incidence
The number of new health related events in a defined population within a specified period of time.
Cumulative Incidence (CI)
Measures the proportion of people with disease at start of specified time period
CI = Number who develop disease in specified time period / Number at risk of getting disease at start of time period
Expressed as proportion or percentage
Incidence Rate (IR)
Measure how quickly people are developing the disease
IR = Number who develop disease / number person-time when people were at risk of getting disease
Expressed as a function of time (i.e person years)
Person-Time
The product of the amount of time multiplied by the number of members of a population who have been affected by a certain condition.
Each person contributes one person-year to the denominator for each year (or day, week, month) of observation before disease develops or is lost to follow-up.
How are prevalence and incidence related?
Depends on how long disease persists before cure or death.
Prevalence = Incidence rate x average duration of disease
Assumes a stationary population and prevalence of disease is rare
What increases prevalence?
o Long duration of disease o Incidence rate increase o In-migration of cases o In-migration of susceptible/at risk o Out migration of healthy people o Improved diagnostics / better reporting
What decreases prevalence?
o Shorter duration o High case-fatality o Decrease in incidence o In-migration of healthy people o Out-migration of cases o Improved cure rate
How to calculate Mortality Rate?
Number of deaths in a given period / population at risk of death over that period
How to calculate survival rate?
Number of patients still alive from diagnosis to given period / total number of patients over that period.
What are some of the ‘Total Health Measures’?
Burden of Disease Life Expectancy Disability-Free Life Expectancy Quality Adjusted Life Years Health Adjusted Life Expectancy