Flashcards in Probability and Statistics Deck (9)
Define risk and relative risk.
Risk is the probability that something will happen. So, the number of occurrences on one event divided by the total number of occurrences of events.
Risk ratio or relative risk is the ratio of one risk over another.
Define odds and odds ratio.
Odds is the number of occurrences of an event divided by the number of nonoccurrences.
Odds ratio is the ratio of two odds.
How to calculate and differentiate the risk and the odds?
To calculate risk, we divide the number of intended event by the total row frequency (event/total in the same exposure or characteristic).
To calculate odds we divide the number of intended event by the number of observations in the other cell of that row (event/nonevent in the same exposure or characteristic).
What are mutually exclusive events?
The occurrence of one event precludes the occurrence of the other. You have one outcome or the other, but not both.
What is the multiplicative rule?
The probability of one event followed by another is the probability of the first event times the probability of the second event, assuming that the events are independent.
What is the additive rule?
The probability of the occurrence of one or another of two mutually exclusive events is the sum of the two probabilities.
Give an example of a conditional probability.
The probability that it will snow given that the temperature is below 32 degrees is .20.
How do we signify conditional probabilities?
We place a vertical bar between the two events. For example, p(snow | below 32°).