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

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

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

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

cohort study

• observational, analytic study

• starting point is exposure

cohort

group of persons with common defining characteristic

RR > 1

association: exposed group have higher risk of outcome than unexposed group

RR = 1

no association

RR < 1

inverse association: exposed group have lower risk of outcome than unexposed group

population

who we want to learn about

sample

who we will study

case-control study

• observational, analytic study

• starting point is outcome (i.e. disease)

cases

individuals with outcome or disease

controls

individuals without the outcome or disease

experimental studies

• evaluate specific intervention (exposure)

• assign study groups

• create a controlled environment such that the only thing that is different between study groups is exposure status

randomized

• assignment to study groups is by chance

• not under control of investigator

non-randomized

assignment to study groups is under control of investigator

randomized controlled trials

experimental study to assess the efficacy of an intervention in humans

efficacy

ability to achieve a desired effect under highly controlled conditions

effectiveness

do interventions work in circumstances that reflect real-world practice

concealment of allocation

procedure to protect the randomization before patients are entered into a trial

blinding

masking of the allocation after randomization of patients

single-blinded

patient does not know which study group they are allocated to

double-blinded

patient and researcher do not know which study group patients are allocated to

internal validity

how well was the study conducted?

external validity

how applicable are study findings?

confounding

confusion, or mixing, of effects; the effects of the exposure is mixed together with the effect of another variable, leading to distortion of the measure of association

confounder

some other factor that also associated with the outcome

stratified analysis

analysis according to strata (groups) of a factor/characteristic of participants