Biostats Flashcards
What is frequency of disease in population?
prevalence, incidence, and attack rate
How well does test differentiate sick from healthy?
sensitivity and specificity
Of those in population who test as sick or healthy, how true is that?
Predictive value
What is impact of medicine/treatment?
Risk reduction/increase
NNT, NNH
Prevalence
helps understand disease burden or extent of health problem
= # of people with disease at specific point/# of people AT RISK for illness at same point in time
Period prevalence
during a period of time (specific)
Lifetime prevalence
over course of a lifetime
Incidence
helps understand risk of specific health event
= # of NEW people with disease during time period/# of people at risk for illness during time period
if you already have disease -> not at risk anymore
Cumulative incidence
total number reported over time
Attack Rate
type of incidence used during short period of time (specific exposures/outbreaks)
= # new cases/#exposed
Secondary Attack Rate
= # of new cases/(# exposed - primary cases)
- measures person-to-person spread of disease after initial exposure
What affects prevalence and incidence?
Duration of illness (higher prevalence) Number of new cases (higher prevalence) Ill people coming in (higher prevalence) Healthy people leaving (higher prevalence) Recovery/death (lower prevalence) Prevention (lower incidence) Changes in diagnostic criteria
Relationship between prevalence and incidence
Chronic illness –> prevalence = incidence x average duration
Acute illness –> prevalence = incidence
Sensitivity
probability that diseased person will be ID correctly (true-positive)
= true positives/ total # ill people (TP and FN)
True positives = ill people ID as ill
False negative = ill people ID as healthy
Specificity
probability that well person will be ID correctly (true-negative)
= true negative/ total # well people (TN and FP)
True negative = healthy people ID as healthy
False positive = healthy people ID as ill
