Disease Occurrence

Question 1

describe descriptive epidemiology

Answer 1

1. describe frequencies
2. what, why, who, when, where, how

Question 2

define ratio, proportion, and rate

Answer 2

ratio: comparison among two groups
-odds ratio = odds in exposed/odds in unexposed

proportion: comparison of a part to a whole
=number affected/total population

rate: a ratio of part to the whole per unit time
=number affected per unit time/total population

-proportions and rates are a type of ratio with the numerator included in the denonimator

Question 3

define prevalence

Answer 3

number of cases in population at specific time

-a snapshot in time at a specific time
-NOT a measure of risk
-informs about burden of disease in population

-point prevalence: prevalence of disease at a SINGLE point in time

-period prevalence: prevalence during a define period of time

Question 4

define incidence

Answer 4

number of NEW cases in population during risk period

-specific to period of observation
-expressed as person-time (cow-time)

consider:
-incidence rate: number of new cases in population per unit of time
-incidence proportion: proportion of new cases in population during period of time

-better for causal association than prevalence!

Question 5

compare and contrast prevalence versus incidence

Answer 5

prevalence:
-number of EXISTING cases of disease at a point in time
-presence/absence of disease in a snapshot of time
-estimates probability of population being ill at period of time in study
-useful to study the burden of disease

incidence:
-number of NEW cases in a specified PERIOD of time
-looks at time of onset of disease
-expresses the risk or speed of becoming ill
-useful for acute or chronic conditions and MORE useful for causation
-measures RISK!!!

Question 6

define attack rate and mortality rate

Answer 6

attack rate = number affected/number at risk

mortality rate = number of deaths/population