risk and summary measures for binary data (3/11) Flashcards
Proportions are…
a special example of a ratio here the numerator is a subset of the denominator
Proportions can be expressed as…
a percentage or fraction or decimal
Define: Rate
is Proportion related to time
Define: Risk
A proportion used to count events which which happen prospectively (find out what is going to happen rather than what has already happened).
Define: ARD (absolute risk difference)
the risk difference (the difference in risk in the control and test group) when one ignores the +ve or -ve
ARD =| pTest – pControl| Where the symbols |...| mean to take the absolute value
Define: absolute risk reduction (ARR)
If we anticipate that the exposure/treatment will reduce some bad outcome (such as deaths).
Define: absolute risk excess (ARE)
If we anticipate that the exposure/treatment will increase some bad outcome (such as deaths)
NNT can be a value between….
1 and infinity
The lower the NNT value…
the better the intervention
Define: Odds
give equation
the ratio of the probability of occurrence of the event to the probability of non-occurrence.
a/c
Define: Odds Ratio (OR)
give equation
Ratio of odds for test group to the odds for the control group
a/c divided by b/d
ALTERNATIVELY
ad/cb
What does an odds ratio of less than 1 mean?
negative association between exposure and outcome (people in the exposed group less likely to experience outcome of interest).
What does an odds ratio of more than 1 mean?
positive association between exposure and outcome (people in the exposed group more likely to experience outcome of interest).
When the probability of an event happening is are, the OR and RR are….
close/ approximate
The odds ratio of an event occurring is the…. of the event not occurring
inverse
