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Statistics - Multinomial Distribution


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A multinomial experiment is a statistical experiment and it consists of n repeated trials. Each trial has a discrete number of possible outcomes. On any given trial, the probability that a particular outcome will occur is constant.

Formula

Pr=n!(n1!)(n2!)...(nx!)P1n1P2n2...Pxnx

Where −

  • n = number of events

  • n1 = number of outcomes, event 1

  • n2 = number of outcomes, event 2

  • nx = number of outcomes, event x

  • P1 = probability that event 1 happens

  • P2 = probability that event 2 happens

  • Px = probability that event x happens

Example

Problem Statement:

Three card players play a series of matches. The probability that player A will win any game is 20%, the probability that player B will win is 30%, and the probability player C will win is 50%. If they play 6 games, what is the probability that player A will win 1 game, player B will win 2 games, and player C will win 3?

Solution:

Given:

  • n = 12 (6 games total)

  • n1 = 1 (Player A wins)

  • n2 = 2 (Player B wins)

  • n3 = 3 (Player C wins)

  • P1 = 0.20 (probability that Player A wins)

  • P1 = 0.30 (probability that Player B wins)

  • P1 = 0.50 (probability that Player C wins)

Putting the values into the formula, we get:

Pr=n!(n1!)(n2!)...(nx!)P1n1P2n2...Pxnx, Pr(A=1,B=2,C=3)=6!1!2!3!(0.21)(0.32)(0.53), =0.135