Representing risk Flashcards
what is incidence
incidence = freq of new onset cases in a population over a specific period of time
incidence = no. pt who develop disease/no. at risk of disease (over a given time)
how do prevalence + incidence differ
prevalence = freq of all cases
incidence = freq of new cases
so incidence can calculate risk of developing disease
as it detects changes over time
how are prevalence + incidence linked
as incidence increases, prevalence increases
what is person time
person time = freq of people in study x amount of time spent in study
(so 10 people for 10yr = 100 person time)
is person time a valid measurement
NO - risk of chronic disease increases with age
what is a cohort study design
cohort study = 2 groups (exposed, non-exposed)
followed up over time to see outcome
analytical, experimental study
(analytical - testing hypotheses, observational - not manipulating variables)
what are main strengths + weakness of cohort study
strength = good if rare exposure
evidence for cause-effect relationship as temporal precedence
calculates incidence + risk
weakness = bad if outcome rare
expensive - large sample, long duration (people may drop out)
vulnerable to confounding
what is relative + absolute risk
relative = risk of disease in exposed vs non-exposed
if <1 = protected, less risk in exposed group
absolute risk = probability outcome will occur
the more common the disease (even with the same RR), the higher the AR
so common disease becomes a public health issue
what is confidence interval
how precise are estimates (range of values within a given probability that the true value is)
if CI <1, no difference between exposed + non-exposed group
how does CI change with sample size
larger sample size, narrower CI
so more certain there is difference between exposed + non-exposed
