Statistics

mean

x_bar = 1/n Σ x_i

permutation

nPk = n! / (n-k)!

n: size of the set

k: elements drawn

Normal Distribution

Z distribution is a normal distribution with a mean (μ) of 0 and a standard deviation (δ) of 1. Any normal distribution is described by its μ and δ value.

To convert a normal distribution to a Z distribution

 Z = (x - μ) / δ

Standard deviation is the root of the sum of the square errors:

 δ = ( Σ (i - μ)2 ).5

Binomial Distribution

Similar to normal distribution, but for values that can only be discrete.

Probability of an event happening k times given n trials, where p is the probability of n:

 pk(1-p)n-k

Example: The probability of two heads in six coin flips:

 .52(1-.5)6-2 = .25 * .54</sup = 0.015625

Hypothesis Testing

Null hypothesis h₀. Alternate hypothesis H_A or H₁

Single Tail Test

 H0 : μ1 = μ2
 HA : μ1 > μ2

Two Tailed Test

 H0 : μ1 = μ2
 HA : μ1 ? μ2