RISK Flashcards
define risk
probability that an event will occur in a group, whether it be a good or a bad event.
what is p value
probability and refers to the likelihood that the observed difference (or something more extreme) was observed by chance.
define odds
the average frequency of a loss to the average frequency of a win.
Relative Risk is used for
to compare the risk in two different groups of people (e.g. smokers and non-smoker)
Odds Ratio is used for
a measure of association between an exposure and an outcome (e.g. smoking and cancer)
when is RR used
usually used in prospective cohort studies.
when is OR used
case-control studies and sometime in cohort studies (where the incidence is less than 10%).
Absolute Risk is used for
an individual risk of developing a disease over a time period (e.g. smokers and cancer)
number of events (such as a disease) that occurred in a group, divided by the number of people in that group.
what is Relative Risk Reduction
decrease in probability of an event occurring due to a lifestyle change or treatment.
look at contingency tables
look at contingency tables
what is the relative risk formula
A/(A+B) / C(/C+D)
RR = 1 means…
exposure is not associated with the outcome
RR < 1 means…
risk of the outcome is decreased by the exposure;
RR > 1 means…
risk of the outcome is increased by the exposure.
odds ratio equation
(AD) / (BC)
OR = 1 means
exposure is not associated with the outcome
OR < 1 means
there are lower odds of the outcome happening with the exposure
OR > 1 means
there are higher odds of the outcome happening with the exposure
what is a 95% confidence interval (CI)
a range of values that you can be 95% certain contains the true mean of the population
CI analysis
RR or the OR = 1, or the CI = 1, then there is no significant difference between treatment and control groups.
RR/OR >1, and the CI does not include 1, events are significantly more likely in the treatment than the control group.
RR/OR <1, and the CI does not include 1, events are significantly less likely in the treatment than the control group.
When do we use odds and probabilities?
When the outcome is rare (i.e., < 10%) the odds and the probability will be similar. Therefore the OR will provide a reasonable estimation of the RR.
when could the OR be an overestimate of the RR
When the outcome is common in the population (i.e., >10%), the odds will be higher than the probability
treatment seems better than it is
what is AR and AR reduction
AR = size of your own risk
AR reduction = the number of percentage points your own risk goes down if you do something protective
what is the ARR equation
ARR = AR unexposed – AR exposed
negative number
what is another equation for RR based on AR
RR= AR exposed / AR unexposed
what is another equation for RRR based on AR
RRR = (AR unexposed – AR exposed) / AR unexposed
RR and AR should be presented together
RR and AR
how to calculate odds of exposure in case/non case
either a/c
or b/d
