02: epidemiology

rank

order of disease occurrence

count

number of persons who have a given disease

ratio

numerator not necessarily included in denominator

proportion

numerator is necessarily included in the denominator

rate

• numerator = number of ‘events’ observed for a given time

• denominator = population in which events occur, includes time

point prevalence

proportion of a population that has a disease at a specific point in time

period prevalence

proportion of a population that had a disease at any time during a specified period, including pre-existing and new cases

incidence proportion

• numerator = number of new cases of disease over period of time

• denominator = number of individuals at risk for disease at beginning of time period

incidence rate

• numerator = number of new cases of disease over period of time

• denominator = Σ person-time

person-time

time each person was observed

observational studies

• individuals are followed in real-world settings

• no intervention/exposure assignment by researcher

descriptive observational studies

describe occurrence of an outcome

case reports

detailed presentation of 1 case

case series

detailed presentation of 2 or more cases

cross-sectional study

surveys exposures and/or outcomes at a single point in time

descriptive cross-sectional study

• examines patterns

• measures prevalence not incidence

analytic cross-sectional study

• measure association between exposure and disease

• temporal sequence of exposure and outcome impossible to determine

odds

ratio of the number of ways the event can occur to the number of ways the event cannot occur

odds ratio

• numerator = odds of outcome among exposed

• denominator = odds of outcome among unexposed

OR > 1

exposed group have higher odds of outcome compared to unexposed group

OR = 1

no association

OR < 1

exposed group have lower odds of outcome compared to unexposed group