Statistics 528  Lecture 15
1
Statistics 528  Lecture 15
Prof. Kate Calder
1
Assigning Probabilities
Probabilities in a Finite Sample Space
•
Assign a probability to each individual outcome. These probabilities
must be numbers between 0 and 1 and must sum to 1.
•
The probability of any event is the sum of the probabilities of the
outcomes making up the event.
Statistics 528  Lecture 15
Prof. Kate Calder
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How do we determine probabilities?
1.
Frequency of occurrence.
If we repeat a chance experiment many times then,
P(A) = (number of time A occurred)/(number of times
we repeated the experiment)
2.
Assume all outcomes are equally likely
If a random phenomena has k possible outcomes, all equally likely, then each
individual outcome has probability 1/k. The probability of an event A is
P(A) = (count of outcomes in A)/(count of outcomes in S)
= (count of outcomes in A)/k
Statistics 528  Lecture 15
Prof. Kate Calder
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3. Subjective estimates
4. Mathematical model
Statistics 528  Lecture 15
Prof. Kate Calder
4
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 Winter '09
 Calder
 Statistics, Probability, Probability theory, Prof. Kate Calder

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