Probability (6)

Question 1

What is a likelihood scale

Answer 1

A scale that is used to determine how likely something is to happen

Impossible
Very unlikely
Unlikely
Even
Likely
Very likely
Certain

Question 2

What two values does probability fall between

Answer 2

1 - it will certainly happen
0 - it will never happen

Question 3

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)

Answer 3

Number of successful outcomes ÷ total number of outcomes

= 1/6 (answer to die q)

Question 4

What is the expected frequency of an event

Answer 4

The number of times expect the event to happen, over the given number of trials

= P(event) × number of trials

Question 5

What is a trial

Answer 5

Each experiment (or response to a survey)

Question 6

How do you calculate an estimated probability

Answer 6

Number of trials with successful outcomes ÷ total number of trials

Question 7

How can you be more accurate in finding an estimated probability

Answer 7

Increase the number of trials

Question 8

What is absolute risk

Answer 8

The probability of an event happening

Question 9

What is relative risk

Answer 9

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

Question 10

What is a sample space

Answer 10

A list of all possible outcomes - these outcomes are often shown in a sample space diagram

Question 11

What does each region in a venn diagram show

Answer 11

The probability of an outcome

Question 12

What are mutually exclusive events

Answer 12

Events that cannot happen at the same time

Question 13

How do you calculate the probability of two mutually exclusive events

Answer 13

P(A or B) = P(A) + P(B)

Question 14

What does it mean if a set of events is exhaustive

Answer 14

The set contains all the possible outcomes

Question 15

How do you calculate the probability of (A) not occurring

Answer 15

P(A) + P(not A) = 1
So

P(not A) = 1 - P(A)

Question 16

In a venn diagram what does P(A n B) mean

Answer 16

This is the intersection of A AND B - in a venn diagram it is where the groups overlap

P(A and B)

Question 17

In a venn diagram what does P(A u B) mean

Answer 17

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)

Question 18

What is the general addition law for events that arent mutually exclusive

Answer 18

P(A u B) = P(A) + P(B) - P(A n B)

Question 19

For two independent events how do you calculate P(A and B)

Answer 19

P(A) × P(B)

Question 20

What are tree diagrams

Answer 20

A diagram used in probability where each ‘branch’ shows an outcome

Question 21

What is conditional probability

Answer 21

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)

Question 22

What is the formula used to calculate conditional probability

Answer 22

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’)

Question 23

What is P(A’)

Answer 23

Probability of NOT A

You would calculate it by subtracting A from 1

Question 24

How can you use conditional probability to see if two events are independent

Answer 24

If P(B) = p(B|A) the events are independent