measures of occurrence and measures of associations Flashcards
O(occurence)
define the outcome eg
deaths, hospitalisations or symptoms, this is also known as the case definition
O
not use simple counts or different years from different populations
don’t take into account total population
within a population you can make comparisons over time
O
what is risk
measure of the incidence of an outcome
calculated by
no.people developed new outcomes / no. people at risk
O
risk denominator doesn’t include
people who already have the disease and certain populations who can’t develop the outcome eg men and cervical cancer
O
what is rate
measure of incidence calculated by
no. new outcomes / total at risk follow up time
O
incident rate for chronic event/disease
or for recurrent event
No. event / total person time
number of times(or weeks) / total (weeks not ill)
O
population studies often use mid year population why
assuming random migration and no seasonal pattern it is used to approximate the total person-year of that population
O
prevalence differs from rate or risk how
and what is used for?
not on new cases, focuses on all existing cases at a given time
used to describe the proportion of people with the outcome at a specific time point (point prevalence)
O
prevalence
no. people with the outcomes / no. people at risk
O
relationship between prevalence incident rate and duration
P = IR x D
O
prevalence decreases if
IR decreases eg less new cases, healthy immigration, ill out migration
D decreases eg high fatality or improved cure rate
O
odds ratios used as a measure of association
odds= prob. occurring / prob. not occurring
Uses of occurrence -
prevalence used for proportion of people with outcome - useful resource allocation
risk better for fixed pop. or rarer events
rate better for dynamic pop. or common events
Associations useful for
quantifying relationship between health events (outcome) and relevant factors (exposure)
