Flashcards in Behavioural and Biostats Deck (20):
Collects data from a group of people to assess frequency of disease and related risk factors at a particular point in time
cross sectional study
compares a group of people with disease to a group without disease to look for prior exposures or risk factors
compares a group with a given exposure or risk factor to a group without such exposure to see if exposure increased likelihood of disease
case control study calculates what
cohort study calculates what
cross sectional study calculates what
prevalence (NOT incidence)
clinical trial phase: is it safe?
phase 1, small number of healthy volunteers
clinical trial phase: does it work?
phase 2: small number of patients with disease of interest
clinical trial phase: is it as good or better?
phase 3: large number of patients randomly assigned to either treatment or placebo/best treatment available
clinical trial phase: can it stay?
phase 4: postmarketing surveillance of patients after treatment is approved
how does prevalence affect PPV and NPV?
increasing prevalence increases PPV and decreases NPV
odds ratios are used in what kind of studies
relative risk is used in what studies
how many people with disease had exposure
A/C / B/D
how many people with exposure got disease
a/(a+b) / c/(c+d)
Attributable risk formula
proportion of disease attributable to the exposure
a/a+b - c/c+d
relative risk reduction formula
proportion of risk reduction attributable to intervention
absolute risk reduction forumula
difference in risk attributable to intervention vs. control
c/c+d - a/a+b
number needed to treat formula
number of patients who need to be treated for1 1 person to benefit