Conditional Probability(์กฐ๊ฑด๋ถ ํ๋ฅ ):
This is defined as the probability of an event occurring, assuming that one or more other events have already occurred.
์กฐ๊ฑด๋ถ ํ๋ฅ ์ ํ๋ ์ด์์ ์ฌ๊ฑด์ด ์ด๋ฏธ ์ผ์ด๋ ํ์ ์ด๋ ํ ์ฌ๊ฑด์ด ๋ฐ์ํ ํ๋ฅ ์ด๋ค.
Two events, A and B are considered to be independent if event A has no effect on the probability of event B.
์ฌ๊ฑด A๊ฐ ์ฌ๊ฑด B์ ์ํฅ์ ๋ฏธ์น์ง ์๋๋ค๋ฉด, ๋์ฌ๊ฑด A์ B๋ ๋ ๋ฆฝ์ ์ด๋ค.
If events A and B are not independent, then we must consider the probability that both events occur.
This can be referred to as the intersection of events A and B,
We can then use this definition to find a conditional probability.
Dividing the probability of the intersection of the two events by the probability of the event that is assumed to have already occurred.
์ฐ๋ฆฌ๋ ์์ ์ ์๋ฅผ ์ด์ฉํด์ ์กฐ๊ฑด๋ถ ํ๋ฅ ์ ๊ตฌํ ์ ์๋ค.
์ด๋ฏธ ๋ฐ์ํ ์ฌ๊ฑด์ผ๋ก ์ถ์ ๋๋ ์ฌ๊ฑด์ ํ๋ฅ ๋ก ๋ ์ฌ๊ฑด์ ๊ต์งํฉ์ ํ๋ฅ ์ ๋๋๋ค.
Bayes' Theorem(๋ฒ ์ด์ง์ ์ ๋ฆฌ):
P( A | B ) denotes the probability of the occurrence of A given that B has occurred ( B๊ฐ ๋ฐ์ํ๋ฉด, A๊ฐ ๋ฐ์ ํ ํ๋ฅ )
P( B | A ) denotes the probability of the occurrence of B given that A has occurred ( A๊ฐ ๋ฐ์ํ๋ฉด, B๊ฐ ๋ฐ์ ํ ํ๋ฅ )
Let A and B be two events such that P( A | B ) and P( B | A ),
A์ B๊ฐ P( A | B ) ๊ทธ๋ฆฌ๊ณ P( B | A ) ๋ผ๋ฉด,