Useful Discrete Random Variable The University of Texas at Dallas Useful Discrete Random Variable Duncan MacFarlane The University of Texas at Dallas
Distributions and their uses Bernoulli – Number of successes on one trial Geometric – Number of trials until first success Binomial – Number of successes on n trials Pascal – Number of trials until the k-th success Poisson – Arrival statistics
Bernoulli and Geometric Distributions Number of successes on one trial P(x) = (1-p) for x=0, or P(x) = p for x=1 Geometric Number of trials until first success P(x) = p(1-p)(n-1)
Geometric PMF
Geometric CDF
Binomial Distribution Binomial – Number of Successes on n trials
Binomial PMF, n=10
Binomial CDF n=10
Pascal Distribution Pascal – Number of trials until the k-th success For n=k, k+1, k+2 ….
Arrival Statistics (busses, customers, etc) Poisson Distribution Arrival Statistics (busses, customers, etc) A: is the average arrival rate times the observation time A=T
Poisson PMF
Poisson CDF
Distribution E(X) Var(X) Summary Distribution E(X) Var(X) Bernoulli p p(1-p) Geometric 1/p (1-p)/p2 Binomial np np(1-p) Pascal k/p p(1-p)/p2 Poisson A