# STAB22 - Highly detailed Chapter 15 Notes, Summer 2012, Ken Butler

STAB22 - CHAPTER15 - PROBABILITY RULES!

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WHERE ARE WE GOING?

CONDITIONAL PROBABILITY

- ex. probability of car accident happening given the person is

- a senior

- a teenager

- young adult

- probability of an event can change when more is learned about relevant situation

PROBABILITY ON CONDITION

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[1]

(ex) What is the name of the home province of a travelling Canadian to Stonehenge,

England?

S = {Alberta, BC, Manitoba, NFL and Labrador, NWT, Nova Scotia, Nunavut, Ontario,

PEI, Quebec, Saskatchewan, Yukon}

- probability of meeting some1 from Ontario is not the same as probability of meeting

some1 from Nunavut

=> diff. outcomes listed in sample space are NOT equally likely

[2]

- how can these outcomes be combined in diff ways to make diff. events?

(ex)

A = {New Brunswich, NFL & Labrador, Nova Scotia, PEI} => event that person's home

province is one of the Atlantic provinces

B = {New Brunchswick, NWT, Nunavut, Quebec, Yukon} => event that person's home

province has official lang. being French

[3]

- probabilities of events A and B?

- outcomes in sample space in this situation are not equally likely

=> despite event A having 4 outcomes, each one will not have probability 1/13

to yield 4/13 in total for event.

=> same situation goes for B: does not total to 5/13

CONDITIONAL PROBABILITY - It Depends..

[1]

(ex) contingency table showing distrubution of official language by region

- gives counts of visitors by:

- cvar1: official lang &

- cvar2: region of residence

P(French) = 69/248 = 0.2782

=> probability that we select French speaker from entire group of visitors = its

corresponding relative freq.

- b/c it is equally likely to select any of 248 ppl at random

P(French and Atlantic) = 0.0362

P(Quebecer) = 0.221774193

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## Document Summary

Ex. probability of car accident happening given the person is. Probability of an event can change when more is learned about relevant situation. [1] (ex) what is the name of the home province of a travelling canadian to stonehenge, S = {alberta, bc, manitoba, nfl and labrador, nwt, nova scotia, nunavut, ontario, Probability of meeting some1 from ontario is not the same as probability of meeting some1 from nunavut. => diff. outcomes listed in sample space are not equally likely. How can these outcomes be combined in diff ways to make diff. events? (ex) A = {new brunswich, nfl & labrador, nova scotia, pei} => event that person"s home province is one of the atlantic provinces. B = {new brunchswick, nwt, nunavut, quebec, yukon} => event that person"s home province has official lang. being french. Outcomes in sample space in this situation are not equally likely.