Probability (6) Flashcards
What is a likelihood scale
A scale that is used to determine how likely something is to happen
Impossible
Very unlikely
Unlikely
Even
Likely
Very likely
Certain
What two values does probability fall between
1 - it will certainly happen
0 - it will never happen
How do you calculate the probability of an event, if all outcomes are equally likely, E.g p(rolling a 1 on a fair 6 sided die)
Number of successful outcomes ÷ total number of outcomes
= 1/6 (answer to die q)
What is the expected frequency of an event
The number of times expect the event to happen, over the given number of trials
= P(event) × number of trials
What is a trial
Each experiment (or response to a survey)
How do you calculate an estimated probability
Number of trials with successful outcomes ÷ total number of trials
How can you be more accurate in finding an estimated probability
Increase the number of trials
What is absolute risk
The probability of an event happening
What is relative risk
How many more times an event is likely to happen over another event.
Relative risk for a group = relative risk for those in the group ÷ risk for those not in the group
What is a sample space
A list of all possible outcomes - these outcomes are often shown in a sample space diagram
What does each region in a venn diagram show
The probability of an outcome
What are mutually exclusive events
Events that cannot happen at the same time
How do you calculate the probability of two mutually exclusive events
P(A or B) = P(A) + P(B)
What does it mean if a set of events is exhaustive
The set contains all the possible outcomes
How do you calculate the probability of (A) not occurring
P(A) + P(not A) = 1
So
P(not A) = 1 - P(A)
In a venn diagram what does P(A n B) mean
This is the intersection of A AND B - in a venn diagram it is where the groups overlap
P(A and B)
In a venn diagram what does P(A u B) mean
The union of A and B
It is the probability that either A, or B or BOTH of them occur
In a venn diagram all of the circles would be shaded
p(A or B)
What is the general addition law for events that arent mutually exclusive
P(A u B) = P(A) + P(B) - P(A n B)
For two independent events how do you calculate P(A and B)
P(A) × P(B)
What are tree diagrams
A diagram used in probability where each ‘branch’ shows an outcome
What is conditional probability
The probability of an event occurring, given that something else has happened
The probability B will happen given that A has happened is written as
P(B|A)
What is the formula used to calculate conditional probability
P(B|A) = P(A and B) ÷ P(A)
You divide the total of the two probabilities that have occurred by the action/probability that has already occurred
P(B|A’) = P( B and A’) ÷ P(A’)
What is P(A’)
Probability of NOT A
You would calculate it by subtracting A from 1
How can you use conditional probability to see if two events are independent
If P(B) = p(B|A) the events are independent
