Week 3 Measures of DIsease Module Flashcards
what is the problem with counts?
a count does not give you a denominator, does not relate to the total population
when is a count useful?
resources need to be allocated to treat/follow disease
what is a ratio?
compares relative size of two values. ex: boys/girls at birth
what is a proportion?
a ratio in which the numerator is a subset of the denominator. Ex: proportion of boys: (boys/(boys+girls))
a medical school has a class with 60 males and 40 females. what is the proportion male? ratio of females/males
proportion male: 60/100
ratio of females/males: 60/40
what is a rate?
a ratio that takes the from a/a+b during some period of time
epidemiologic rates contain (3)
count of disease frequency, size of the popn at risk, time period during which the disease occurred in the reference population
what is a fixed population
membership is permanent and define by an event/charactestic. the number doesn’t change. ex: babies born at Wexner in 2012
what is a dynamic population?
membership is changing. citizens of monroe county
what are the two most important measures of disease frequency?
incidence and prevelance
Incidence:
number of new cases over a period of time.
cumulative incidence:
number of new cases/# at risk at beginning of follow-up over a specified period of time. assumes popn are fixed (flaw)
what is the incidence rate (density)
of new cases/ sum of disease-free person-time over a specified period (alllows populations to be dynamic)
how do you calculate person-years 3
add the individual risk periods (exact, count up number of years total), use the average number of people in study x the study duration, use the average duration x number of people
prevelance
the proportion of people in a popn with the disease a a specified point or period in time. measures existing cases
