disease frequency Flashcards
two types of populations
fixed
dynamic
3 types of calculations in frequencies
Ratio
Proportion
Rate
what is a ratio?
division of 2 numbers that are not related
ex sex ratio
what is proportion
division of 2 numbers (numerator the subset of denominator)
what is rate
Division of 2 numbers (time is always in the denominator)
what is incidence
measures new cases of disease that develop in a population at risk over a period of time
what is prevalence
measures existing cases of a disease at a particular point of time or during a period time
what are the 2 types of prevalence
point prevalence
period prevalence
what is point prevalence?
measures the freq of disease at a given point of in time
P=C/N
C= #of observed at time
N=population size at time t
period prevalence
PP= (C+I)/N
c- the # of prevalent cases at beginning of time period
i- the # of incident cases that develop during period
n- size of population for this same time period
what are the 3 things to consider when evaluating incidence
1- new disease events, or for diseases that can occur more than once, usually first occurrence of disease
2-population is at risk (can’t have disease already)
3- time must pass for a person to move from health to disease
describe cumulative incidence (2 other synonyms)
CI AKA Risk!!!
aka incidence proportion
can be calculated w fixed populations or no loss to follow up
describe incidence rate (2 other synonyms)
aka rate or incident density
person time always in denominator
good for dynamic populations
CI= I/N
i- # of new cases of disease during followup
n- #of disease-free subjects at the start of follow up
estimate of individual risk
