Measurements
Prevelance
Incidence
proportion = of population with the outcome or exposure at a certain point in time
count of all cases in a time period/point, defined population and place
used to allocate resources and services
gives extent of a health problem in population
NOT possible cause of outcome
NOT effectiveness of intervention
measures the burden of a disease in a population
= number of cases (in the whole population)/total population
period
point
lifetime
= number of all cases (old+new) at a time point/total population at time point
eg, 1 day
= number of all cases (old+new) over time period/total population over time period
eg, 1 or 12 months
= number of cases who ever had disease/total population (at beginning of study)
useful for chronic disease, with long duration of onset
influenced by
rates of recovery, death and migration
incidence of cases
new measures of detection - these tend to fine more cases, prevelance increases
measure of new cases over time
can identify causes of outcome/disease
used to evaluation effectiveness of treatments or interventions
person
place
time
age, gender, race, ethnicity
genetics
comorbidities
lifestyle
SES, education, occupation
accommodation
place of occupation
population density
economic development
healthcare availability
time of day
time since an event
date of onset
age
seasonality
trends
cumulative incidence/indicence proportion
incidence rate
proportion of an initially disease-free population that develops disease
determines risk factors
demominator
numerator
= case(s)
criteria to become a case must be specific
diagnosis can change due to information sources and advances in medicine
= population
all members of a group defined by a common characteristic
= number of cases in a time period/number of population at risk at the start of the time period
denominator is in person-time
how long did it take for the disease to develop
takes length of exposure into consideration
= number of new cases/total 'person-time' of observation