Stats GCSE Probability

Number of successful outcomes/total number of possible outcomes

How to calculate P(event)

Something that can happen as a result of a trial

What’s an outcome?

The number of times you expect an event to happen

What’s the expected frequency?

P(outcome)\*number of trials

How to calculate expected frequency

no. of trials with success/total no. of trials

How to calculate estimated probability

Number of trials

What increases the reliability of estimated probability?

Relative frequency

What’s another way to say estimated probability?

The probability of an event occurring for negative events

What’s the risk?

No. of trials where event happens/total no. of trials

How to calculate risk of event

How likely an event is to happen

What’s the absolute risk?

How much more likely an event is to happen for one group compared to another group

What is relative risk?

Risk for those in the group/risk for those not in the group

How to calculate relative risk

Events that cannot happen at the same time

What are mutually exclusive events?

The set contains all the possible outcomes

What does exhaustive mean?

1

In mutually exclusive and exhaustive events, what’s the sum of the probabilities?

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

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

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

What is the addition law for ME events?

Mutually exclusive events

What doesn’t the general addition law not apply for?

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

What’s the general addition law?

The intersect

How is P(A and B) represented on a Venn diagram?

Everything in both circles

How is P(A or B) represented on a Venn diagram?

Unconnected events

What are independent events?

P(A and B)=P(A)\*P(B)

What’s the rule for 2 independent events?

P(A and B and C)=P(A)\**P(B)**P(C)

What’s the rule for 3 independent events?

When one event affects the other

What’s conditional probability?

The probability of B given that A happened

What does P(B|A) mean?

If phrases like ‘given that’ or ‘if’ are used

How can you tell if something’s conditional probability?

P(A and B)/P(B)

How to calculate P(B|A)

P(B|A)\*P(A)

How to calculate P(A and B)

The events are conditional, not independent

What does if mean if P(A) isn’t equal to P(A|B)?