CHAPTER 6 Flashcards
what is probability?
- a numerical measure of the chance of an event happening
what does it mean if a probability is 0?
- impossible for the event to happen
what does it mean if a probability is 1?
- the event is certain to happen
how can you write probabilities?
- as fractions
- as decimals
- as percentages
probability of an event equation:
probability of an event= number of successful outcomes/ total number of possible outcomes
expected frequency equation:
expected frequency of an event A= P(A) x number of trials
what is the expected frequency?
- the number of times you expect the event to happen
- it is not necessarily what actually will happen
what is a trial?
- each experiment (or response to a survey)
estimated probability equation:
estimated probability= number of trials with successful outcome/ total number of trials
risk of an event equation:
risk of event= number of trials in which event happens/ total number of trials
what is the absolute risk?
- the probability of an event happening
what is the relative risk?
- how many times more likely an event is to happen for one group compared to another group
relative risk for a group equation?
risk for those in the group/ risk for those not in the group
what is a list of all the possible outcomes called?
- sample space (S)
what conditions must be met for a sample space diagram?
- the outcomes must be equally likely
- can use if there are two events
what does each region of a probability Venn diagram represent?
- The probability of a different outcome
what should the sum of probabilities represented in a Venn diagram be?
must equal 1
when are events mutually exclusive?
- they cannot happen at the same time
addition law for two mutually exclusive events:
P (A or B)= P(A)+ P(B)
when is a set of events exhaustive?
- if the set contains all possible outcomes
when is the sum of all the probabilities 1?
- for a set of mutually exclusive, exhaustive events, the sum of all of the probabilities is equal to 1
how do you write the probability of an event not happening?
P(not A)
how to work out P(A):
P(A) + P(not A)= 1
how to work out P(not A):
P(not A)= 1- P(A)
general addition law for events which are not mutually exclusive:
- P(A U B)= P(A) + P(B)- P(A intersection B)
what does each branch of a tree diagram represent?
- an outcome
- the probability of the outcome is written on the branch
when are two events conditional?
- if the outcome of one event affects the outcome of the other event
- conditional events are not independent
conditional probability:
- the probability that B will happen if A has happened the conditional probability if B given A
- it is written P(B|A)
formula for conditional probability of B given A:
P(B|A)= P(A and B)/ P(A)
formula for the probability of A and B:
P(A and B)= P(B|A) x P(A)
formula for testing if two events are independent:
P(A)= P(A|B)
- if P(A) and P(A|B) are not equal the events are not independent (they are conditional)
