Chapter 5 Notes

updated 9/30/2014

©2008 by S. Gramlich

Probability Distribution

! = Important Note

! These Notes are not meant to replace Reading. Read Chapter first.

5-2

Probability Distribution (PD) Requirements:

1) X discrete

2) 0 <= P(X) <= 1

3) ∑ P(X) = 1

if the PD meets the above requirements then proceed with finding the following parameters:

mean: μ = ∑[x * P(x)]

variance: σ² = ∑[(x-μ)² * P(x)]

standard deviation: σ = √σ²

! I am citing Formula 5-2 from text but may have to use Formula 5-3 instead to get same answer in HW

Range Rule of Thumb (Confidence Interval) for finding interval of usual scores:

max = μ + 2*σ

min = μ - 2*σ

so any # outside of the usual interval [min, max] is considered unusual.